diff --git a/packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js b/packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js
index bc3a7c36eb7db..371a1dd229430 100644
--- a/packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js
+++ b/packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js
@@ -81,6 +81,7 @@ import {
   completeBoundaryWithStyles as styleInsertionFunction,
   completeSegment as completeSegmentFunction,
   formReplaying as formReplayingRuntime,
+  markShellTime,
 } from './fizz-instruction-set/ReactDOMFizzInstructionSetInlineCodeStrings';
 
 import {getValueDescriptorExpectingObjectForWarning} from '../shared/ReactDOMResourceValidation';
@@ -120,13 +121,14 @@ const ScriptStreamingFormat: StreamingFormat = 0;
 const DataStreamingFormat: StreamingFormat = 1;
 
 export type InstructionState = number;
-const NothingSent /*                      */ = 0b000000;
-const SentCompleteSegmentFunction /*      */ = 0b000001;
-const SentCompleteBoundaryFunction /*     */ = 0b000010;
-const SentClientRenderFunction /*         */ = 0b000100;
-const SentStyleInsertionFunction /*       */ = 0b001000;
-const SentFormReplayingRuntime /*         */ = 0b010000;
-const SentCompletedShellId /*             */ = 0b100000;
+const NothingSent /*                      */ = 0b0000000;
+const SentCompleteSegmentFunction /*      */ = 0b0000001;
+const SentCompleteBoundaryFunction /*     */ = 0b0000010;
+const SentClientRenderFunction /*         */ = 0b0000100;
+const SentStyleInsertionFunction /*       */ = 0b0001000;
+const SentFormReplayingRuntime /*         */ = 0b0010000;
+const SentCompletedShellId /*             */ = 0b0100000;
+const SentMarkShellTime /*                */ = 0b1000000;
 
 // Per request, global state that is not contextual to the rendering subtree.
 // This cannot be resumed and therefore should only contain things that are
@@ -4107,21 +4109,53 @@ function writeBootstrap(
   return true;
 }
 
+const shellTimeRuntimeScript = stringToPrecomputedChunk(markShellTime);
+
+function writeShellTimeInstruction(
+  destination: Destination,
+  resumableState: ResumableState,
+  renderState: RenderState,
+): boolean {
+  if (
+    enableFizzExternalRuntime &&
+    resumableState.streamingFormat !== ScriptStreamingFormat
+  ) {
+    // External runtime always tracks the shell time in the runtime.
+    return true;
+  }
+  if ((resumableState.instructions & SentMarkShellTime) !== NothingSent) {
+    // We already sent this instruction.
+    return true;
+  }
+  resumableState.instructions |= SentMarkShellTime;
+  writeChunk(destination, renderState.startInlineScript);
+  writeCompletedShellIdAttribute(destination, resumableState);
+  writeChunk(destination, endOfStartTag);
+  writeChunk(destination, shellTimeRuntimeScript);
+  return writeChunkAndReturn(destination, endInlineScript);
+}
+
 export function writeCompletedRoot(
   destination: Destination,
   resumableState: ResumableState,
   renderState: RenderState,
+  isComplete: boolean,
 ): boolean {
+  if (!isComplete) {
+    // If we're not already fully complete, we might complete another boundary. If so,
+    // we need to track the paint time of the shell so we know how much to throttle the reveal.
+    writeShellTimeInstruction(destination, resumableState, renderState);
+  }
   const preamble = renderState.preamble;
   if (preamble.htmlChunks || preamble.headChunks) {
     // If we rendered the whole document, then we emitted a rel="expect" that needs a
     // matching target. Normally we use one of the bootstrap scripts for this but if
     // there are none, then we need to emit a tag to complete the shell.
     if ((resumableState.instructions & SentCompletedShellId) === NothingSent) {
-      const bootstrapChunks = renderState.bootstrapChunks;
-      bootstrapChunks.push(startChunkForTag('template'));
-      pushCompletedShellIdAttribute(bootstrapChunks, resumableState);
-      bootstrapChunks.push(endOfStartTag, endChunkForTag('template'));
+      writeChunk(destination, startChunkForTag('template'));
+      writeCompletedShellIdAttribute(destination, resumableState);
+      writeChunk(destination, endOfStartTag);
+      writeChunk(destination, endChunkForTag('template'));
     }
   }
   return writeBootstrap(destination, renderState);
@@ -5015,6 +5049,21 @@ function writeBlockingRenderInstruction(
 
 const completedShellIdAttributeStart = stringToPrecomputedChunk(' id="');
 
+function writeCompletedShellIdAttribute(
+  destination: Destination,
+  resumableState: ResumableState,
+): void {
+  if ((resumableState.instructions & SentCompletedShellId) !== NothingSent) {
+    return;
+  }
+  resumableState.instructions |= SentCompletedShellId;
+  const idPrefix = resumableState.idPrefix;
+  const shellId = '\u00AB' + idPrefix + 'R\u00BB';
+  writeChunk(destination, completedShellIdAttributeStart);
+  writeChunk(destination, stringToChunk(escapeTextForBrowser(shellId)));
+  writeChunk(destination, attributeEnd);
+}
+
 function pushCompletedShellIdAttribute(
   target: Array<Chunk | PrecomputedChunk>,
   resumableState: ResumableState,
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundary.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundary.js
index 1cbe1e222af91..44a81c64468e7 100644
--- a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundary.js
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundary.js
@@ -2,4 +2,6 @@ import {completeBoundary} from './ReactDOMFizzInstructionSetShared';
 
 // This is a string so Closure's advanced compilation mode doesn't mangle it.
 // eslint-disable-next-line dot-notation
+window['$RB'] = [];
+// eslint-disable-next-line dot-notation
 window['$RC'] = completeBoundary;
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineShellTime.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineShellTime.js
new file mode 100644
index 0000000000000..9e52a25aa7a54
--- /dev/null
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineShellTime.js
@@ -0,0 +1,5 @@
+// Track the paint time of the shell
+requestAnimationFrame(() => {
+  // eslint-disable-next-line dot-notation
+  window['$RT'] = performance.now();
+});
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetExternalRuntime.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetExternalRuntime.js
index 2481752425c46..845ea5b5666e3 100644
--- a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetExternalRuntime.js
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetExternalRuntime.js
@@ -13,9 +13,26 @@ import {
 // This is a string so Closure's advanced compilation mode doesn't mangle it.
 // These will be renamed to local references by the external-runtime-plugin.
 window['$RM'] = new Map();
+window['$RB'] = [];
 window['$RX'] = clientRenderBoundary;
 window['$RC'] = completeBoundary;
 window['$RR'] = completeBoundaryWithStyles;
 window['$RS'] = completeSegment;
 
 listenToFormSubmissionsForReplaying();
+
+// Track the paint time of the shell.
+const entries = performance.getEntriesByType
+  ? performance.getEntriesByType('paint')
+  : [];
+if (entries.length > 0) {
+  // We might have already painted before this external runtime loaded. In that case we
+  // try to get the first paint from the performance metrics to avoid delaying further
+  // than necessary.
+  window['$RT'] = entries[0].startTime;
+} else {
+  // Otherwise we wait for the next rAF for it.
+  requestAnimationFrame(() => {
+    window['$RT'] = performance.now();
+  });
+}
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetInlineCodeStrings.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetInlineCodeStrings.js
index 97a1a7b80a99b..0653761df7594 100644
--- a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetInlineCodeStrings.js
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetInlineCodeStrings.js
@@ -1,12 +1,14 @@
 // This is a generated file. The source files are in react-dom-bindings/src/server/fizz-instruction-set.
 // The build script is at scripts/rollup/generate-inline-fizz-runtime.js.
 // Run `yarn generate-inline-fizz-runtime` to generate.
+export const markShellTime =
+  'requestAnimationFrame(function(){$RT=performance.now()});';
 export const clientRenderBoundary =
   '$RX=function(b,c,d,e,f){var a=document.getElementById(b);a&&(b=a.previousSibling,b.data="$!",a=a.dataset,c&&(a.dgst=c),d&&(a.msg=d),e&&(a.stck=e),f&&(a.cstck=f),b._reactRetry&&b._reactRetry())};';
 export const completeBoundary =
-  '$RC=function(a,d){if(d=document.getElementById(d))if(d.parentNode.removeChild(d),a=document.getElementById(a)){a=a.previousSibling;var f=a.parentNode,b=a.nextSibling,e=0;do{if(b&&8===b.nodeType){var c=b.data;if("/$"===c||"/&"===c)if(0===e)break;else e--;else"$"!==c&&"$?"!==c&&"$!"!==c&&"&"!==c||e++}c=b.nextSibling;f.removeChild(b);b=c}while(b);for(;d.firstChild;)f.insertBefore(d.firstChild,b);a.data="$";a._reactRetry&&a._reactRetry()}};';
+  '$RB=[];$RC=function(e,c){function m(){$RT=performance.now();var f=$RB;$RB=[];for(var d=0;d<f.length;d+=2){var a=f[d],l=f[d+1],g=a.parentNode;if(g){var h=a.previousSibling,k=0;do{if(a&&8===a.nodeType){var b=a.data;if("/$"===b||"/&"===b)if(0===k)break;else k--;else"$"!==b&&"$?"!==b&&"$!"!==b&&"&"!==b||k++}b=a.nextSibling;g.removeChild(a);a=b}while(a);for(;l.firstChild;)g.insertBefore(l.firstChild,a);h.data="$";h._reactRetry&&h._reactRetry()}}}if(c=document.getElementById(c))if(c.parentNode.removeChild(c),e=\ndocument.getElementById(e))$RB.push(e,c),2===$RB.length&&setTimeout(m,("number"!==typeof $RT?0:$RT)+300-performance.now())};';
 export const completeBoundaryWithStyles =
-  '$RM=new Map;\n$RR=function(r,v,w){function t(n){this._p=null;n()}for(var p=new Map,q=document,g,b,h=q.querySelectorAll("link[data-precedence],style[data-precedence]"),u=[],k=0;b=h[k++];)"not all"===b.getAttribute("media")?u.push(b):("LINK"===b.tagName&&$RM.set(b.getAttribute("href"),b),p.set(b.dataset.precedence,g=b));b=0;h=[];var l,a;for(k=!0;;){if(k){var e=w[b++];if(!e){k=!1;b=0;continue}var c=!1,m=0;var d=e[m++];if(a=$RM.get(d)){var f=a._p;c=!0}else{a=q.createElement("link");a.href=d;a.rel=\n"stylesheet";for(a.dataset.precedence=l=e[m++];f=e[m++];)a.setAttribute(f,e[m++]);f=a._p=new Promise(function(n,x){a.onload=t.bind(a,n);a.onerror=t.bind(a,x)});$RM.set(d,a)}d=a.getAttribute("media");!f||d&&!matchMedia(d).matches||h.push(f);if(c)continue}else{a=u[b++];if(!a)break;l=a.getAttribute("data-precedence");a.removeAttribute("media")}c=p.get(l)||g;c===g&&(g=a);p.set(l,a);c?c.parentNode.insertBefore(a,c.nextSibling):(c=q.head,c.insertBefore(a,c.firstChild))}Promise.all(h).then($RC.bind(null,\nr,v),$RX.bind(null,r,"CSS failed to load"))};';
+  '$RM=new Map;$RR=function(r,v,w){function t(n){this._p=null;n()}for(var p=new Map,q=document,g,b,h=q.querySelectorAll("link[data-precedence],style[data-precedence]"),u=[],k=0;b=h[k++];)"not all"===b.getAttribute("media")?u.push(b):("LINK"===b.tagName&&$RM.set(b.getAttribute("href"),b),p.set(b.dataset.precedence,g=b));b=0;h=[];var l,a;for(k=!0;;){if(k){var e=w[b++];if(!e){k=!1;b=0;continue}var c=!1,m=0;var d=e[m++];if(a=$RM.get(d)){var f=a._p;c=!0}else{a=q.createElement("link");a.href=d;a.rel=\n"stylesheet";for(a.dataset.precedence=l=e[m++];f=e[m++];)a.setAttribute(f,e[m++]);f=a._p=new Promise(function(n,x){a.onload=t.bind(a,n);a.onerror=t.bind(a,x)});$RM.set(d,a)}d=a.getAttribute("media");!f||d&&!matchMedia(d).matches||h.push(f);if(c)continue}else{a=u[b++];if(!a)break;l=a.getAttribute("data-precedence");a.removeAttribute("media")}c=p.get(l)||g;c===g&&(g=a);p.set(l,a);c?c.parentNode.insertBefore(a,c.nextSibling):(c=q.head,c.insertBefore(a,c.firstChild))}Promise.all(h).then($RC.bind(null,\nr,v),$RX.bind(null,r,"CSS failed to load"))};';
 export const completeSegment =
   '$RS=function(a,b){a=document.getElementById(a);b=document.getElementById(b);for(a.parentNode.removeChild(a);a.firstChild;)b.parentNode.insertBefore(a.firstChild,b);b.parentNode.removeChild(b)};';
 export const formReplaying =
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetShared.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetShared.js
index 6c21d245b73df..75031bcb5d60a 100644
--- a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetShared.js
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSetShared.js
@@ -47,9 +47,11 @@ export function clientRenderBoundary(
   }
 }
 
+const FALLBACK_THROTTLE_MS = 300;
+
 export function completeBoundary(suspenseBoundaryID, contentID) {
-  const contentNode = document.getElementById(contentID);
-  if (!contentNode) {
+  const contentNodeOuter = document.getElementById(contentID);
+  if (!contentNodeOuter) {
     // If the client has failed hydration we may have already deleted the streaming
     // segments. The server may also have emitted a complete instruction but cancelled
     // the segment. Regardless we can ignore this case.
@@ -57,62 +59,93 @@ export function completeBoundary(suspenseBoundaryID, contentID) {
   }
   // We'll detach the content node so that regardless of what happens next we don't leave in the tree.
   // This might also help by not causing recalcing each time we move a child from here to the target.
-  contentNode.parentNode.removeChild(contentNode);
+  contentNodeOuter.parentNode.removeChild(contentNodeOuter);
 
   // Find the fallback's first element.
-  const suspenseIdNode = document.getElementById(suspenseBoundaryID);
-  if (!suspenseIdNode) {
+  const suspenseIdNodeOuter = document.getElementById(suspenseBoundaryID);
+  if (!suspenseIdNodeOuter) {
     // The user must have already navigated away from this tree.
     // E.g. because the parent was hydrated. That's fine there's nothing to do
     // but we have to make sure that we already deleted the container node.
     return;
   }
-  // Find the boundary around the fallback. This is always the previous node.
-  const suspenseNode = suspenseIdNode.previousSibling;
 
-  // Clear all the existing children. This is complicated because
-  // there can be embedded Suspense boundaries in the fallback.
-  // This is similar to clearSuspenseBoundary in ReactFiberConfigDOM.
-  // TODO: We could avoid this if we never emitted suspense boundaries in fallback trees.
-  // They never hydrate anyway. However, currently we support incrementally loading the fallback.
-  const parentInstance = suspenseNode.parentNode;
-  let node = suspenseNode.nextSibling;
-  let depth = 0;
-  do {
-    if (node && node.nodeType === COMMENT_NODE) {
-      const data = node.data;
-      if (data === SUSPENSE_END_DATA || data === ACTIVITY_END_DATA) {
-        if (depth === 0) {
-          break;
-        } else {
-          depth--;
-        }
-      } else if (
-        data === SUSPENSE_START_DATA ||
-        data === SUSPENSE_PENDING_START_DATA ||
-        data === SUSPENSE_FALLBACK_START_DATA ||
-        data === ACTIVITY_START_DATA
-      ) {
-        depth++;
+  function revealCompletedBoundaries() {
+    window['$RT'] = performance.now();
+    const batch = window['$RB'];
+    window['$RB'] = [];
+    for (let i = 0; i < batch.length; i += 2) {
+      const suspenseIdNode = batch[i];
+      const contentNode = batch[i + 1];
+
+      // Clear all the existing children. This is complicated because
+      // there can be embedded Suspense boundaries in the fallback.
+      // This is similar to clearSuspenseBoundary in ReactFiberConfigDOM.
+      // TODO: We could avoid this if we never emitted suspense boundaries in fallback trees.
+      // They never hydrate anyway. However, currently we support incrementally loading the fallback.
+      const parentInstance = suspenseIdNode.parentNode;
+      if (!parentInstance) {
+        // We may have client-rendered this boundary already. Skip it.
+        continue;
       }
-    }
 
-    const nextNode = node.nextSibling;
-    parentInstance.removeChild(node);
-    node = nextNode;
-  } while (node);
+      // Find the boundary around the fallback. This is always the previous node.
+      const suspenseNode = suspenseIdNode.previousSibling;
 
-  const endOfBoundary = node;
+      let node = suspenseIdNode;
+      let depth = 0;
+      do {
+        if (node && node.nodeType === COMMENT_NODE) {
+          const data = node.data;
+          if (data === SUSPENSE_END_DATA || data === ACTIVITY_END_DATA) {
+            if (depth === 0) {
+              break;
+            } else {
+              depth--;
+            }
+          } else if (
+            data === SUSPENSE_START_DATA ||
+            data === SUSPENSE_PENDING_START_DATA ||
+            data === SUSPENSE_FALLBACK_START_DATA ||
+            data === ACTIVITY_START_DATA
+          ) {
+            depth++;
+          }
+        }
+
+        const nextNode = node.nextSibling;
+        parentInstance.removeChild(node);
+        node = nextNode;
+      } while (node);
+
+      const endOfBoundary = node;
+
+      // Insert all the children from the contentNode between the start and end of suspense boundary.
+      while (contentNode.firstChild) {
+        parentInstance.insertBefore(contentNode.firstChild, endOfBoundary);
+      }
 
-  // Insert all the children from the contentNode between the start and end of suspense boundary.
-  while (contentNode.firstChild) {
-    parentInstance.insertBefore(contentNode.firstChild, endOfBoundary);
+      suspenseNode.data = SUSPENSE_START_DATA;
+      if (suspenseNode['_reactRetry']) {
+        suspenseNode['_reactRetry']();
+      }
+    }
   }
 
-  suspenseNode.data = SUSPENSE_START_DATA;
+  // Queue this boundary for the next batch
+  window['$RB'].push(suspenseIdNodeOuter, contentNodeOuter);
 
-  if (suspenseNode['_reactRetry']) {
-    suspenseNode['_reactRetry']();
+  if (window['$RB'].length === 2) {
+    // This is the first time we've pushed to the batch. We need to schedule a callback
+    // to flush the batch. This is delayed by the throttle heuristic.
+    const globalMostRecentFallbackTime =
+      typeof window['$RT'] !== 'number' ? 0 : window['$RT'];
+    const msUntilTimeout =
+      globalMostRecentFallbackTime + FALLBACK_THROTTLE_MS - performance.now();
+    // We always schedule the flush in a timer even if it's very low or negative to allow
+    // for multiple completeBoundary calls that are already queued to have a chance to
+    // make the batch.
+    setTimeout(revealCompletedBoundaries, msUntilTimeout);
   }
 }
 
diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
index d543d91aedfcf..7f4300f687606 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
@@ -83,6 +83,9 @@ describe('ReactDOMFizzServer', () => {
     global.Node = global.window.Node;
     global.addEventListener = global.window.addEventListener;
     global.MutationObserver = global.window.MutationObserver;
+    // The Fizz runtime assumes requestAnimationFrame exists so we need to polyfill it.
+    global.requestAnimationFrame = global.window.requestAnimationFrame = cb =>
+      setTimeout(cb);
     container = document.getElementById('container');
 
     Scheduler = require('scheduler');
@@ -206,6 +209,7 @@ describe('ReactDOMFizzServer', () => {
     buffer = '';
 
     if (!bufferedContent) {
+      jest.runAllTimers();
       return;
     }
 
@@ -314,6 +318,8 @@ describe('ReactDOMFizzServer', () => {
       div.innerHTML = bufferedContent;
       await insertNodesAndExecuteScripts(div, streamingContainer, CSPnonce);
     }
+    // Let throttled boundaries reveal
+    jest.runAllTimers();
   }
 
   function resolveText(text) {
@@ -602,12 +608,12 @@ describe('ReactDOMFizzServer', () => {
       ]);
 
       // check that there are 6 scripts with a matching nonce:
-      // The runtime script, an inline bootstrap script, two bootstrap scripts and two bootstrap modules
+      // The runtime script or initial paint time, an inline bootstrap script, two bootstrap scripts and two bootstrap modules
       expect(
         Array.from(container.getElementsByTagName('script')).filter(
           node => node.getAttribute('nonce') === CSPnonce,
         ).length,
-      ).toEqual(gate(flags => flags.shouldUseFizzExternalRuntime) ? 6 : 5);
+      ).toEqual(6);
 
       await act(() => {
         resolve({default: Text});
@@ -836,7 +842,7 @@ describe('ReactDOMFizzServer', () => {
         container.childNodes,
         renderOptions.unstable_externalRuntimeSrc,
       ).length,
-    ).toBe(1);
+    ).toBe(gate(flags => flags.shouldUseFizzExternalRuntime) ? 1 : 2);
     await act(() => {
       resolveElement({default: <Text text="Hello" />});
     });
diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js
index 2f63c9695b5d8..578b2bf916f61 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js
@@ -38,6 +38,9 @@ describe('ReactDOMFizzStaticBrowser', () => {
     jest.resetModules();
     JSDOM = require('jsdom').JSDOM;
 
+    // We need the mocked version of setTimeout inside the document.
+    window.setTimeout = setTimeout;
+
     Scheduler = require('scheduler');
     patchMessageChannel(Scheduler);
     act = require('internal-test-utils').act;
@@ -133,13 +136,18 @@ describe('ReactDOMFizzStaticBrowser', () => {
     const temp = document.createElement('div');
     temp.innerHTML = result;
     await insertNodesAndExecuteScripts(temp, container, null);
+    jest.runAllTimers();
   }
 
   async function readIntoNewDocument(stream) {
     const content = await readContent(stream);
-    const jsdom = new JSDOM(content, {
-      runScripts: 'dangerously',
-    });
+    const jsdom = new JSDOM(
+      // The Fizz runtime assumes requestAnimationFrame exists so we need to polyfill it.
+      '<script>window.requestAnimationFrame = setTimeout;</script>' + content,
+      {
+        runScripts: 'dangerously',
+      },
+    );
     const originalWindow = global.window;
     const originalDocument = global.document;
     const originalNavigator = global.navigator;
@@ -167,6 +175,7 @@ describe('ReactDOMFizzStaticBrowser', () => {
     const temp = document.createElement('div');
     temp.innerHTML = content;
     await insertNodesAndExecuteScripts(temp, document.body, null);
+    jest.runAllTimers();
   }
 
   it('should call prerender', async () => {
@@ -980,6 +989,7 @@ describe('ReactDOMFizzStaticBrowser', () => {
     // Wait for the instruction microtasks to flush.
     await 0;
     await 0;
+    jest.runAllTimers();
 
     expect(getVisibleChildren(container)).toEqual([
       <link href="example.com" rel="preconnect" />,
@@ -1611,7 +1621,7 @@ describe('ReactDOMFizzStaticBrowser', () => {
 
     expect(result).toBe(
       '<!DOCTYPE html><html><head><link rel="expect" href="#«R»" blocking="render"/></head>' +
-        '<body>hello<!--$?--><template id="B:1"></template><!--/$--><template id="«R»"></template>',
+        '<body>hello<!--$?--><template id="B:1"></template><!--/$--><script id="«R»">requestAnimationFrame(function(){$RT=performance.now()});</script>',
     );
 
     await 1;
@@ -1636,7 +1646,7 @@ describe('ReactDOMFizzStaticBrowser', () => {
 
     expect(slice).toBe(
       '<!DOCTYPE html><html><head><link rel="expect" href="#«R»" blocking="render"/></head>' +
-        '<body>hello<!--$?--><template id="B:1"></template><!--/$--><template id="«R»"></template>' +
+        '<body>hello<!--$?--><template id="B:1"></template><!--/$--><script id="«R»">requestAnimationFrame(function(){$RT=performance.now()});</script>' +
         '<div hidden id="S:1">world<!-- --></div><script>$RX',
     );
   });
diff --git a/packages/react-dom/src/__tests__/ReactDOMFloat-test.js b/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
index d5e353d9ba2ea..2b7a71b7c7b14 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
@@ -63,6 +63,9 @@ describe('ReactDOMFloat', () => {
     global.Node = global.window.Node;
     global.addEventListener = global.window.addEventListener;
     global.MutationObserver = global.window.MutationObserver;
+    // The Fizz runtime assumes requestAnimationFrame exists so we need to polyfill it.
+    global.requestAnimationFrame = global.window.requestAnimationFrame = cb =>
+      setTimeout(cb);
     container = document.getElementById('container');
 
     React = require('react');
@@ -122,6 +125,7 @@ describe('ReactDOMFloat', () => {
     buffer = '';
 
     if (!bufferedContent) {
+      jest.runAllTimers();
       return;
     }
 
@@ -230,6 +234,9 @@ describe('ReactDOMFloat', () => {
       div.innerHTML = bufferedContent;
       await insertNodesAndExecuteScripts(div, streamingContainer, CSPnonce);
     }
+    await 0;
+    // Let throttled boundaries reveal
+    jest.runAllTimers();
   }
 
   function getMeaningfulChildren(element) {
@@ -729,7 +736,9 @@ describe('ReactDOMFloat', () => {
     });
 
     expect(
-      Array.from(document.getElementsByTagName('script')).map(n => n.outerHTML),
+      Array.from(document.querySelectorAll('script[async]')).map(
+        n => n.outerHTML,
+      ),
     ).toEqual(['<script src="src-of-external-runtime" async=""></script>']);
   });
 
@@ -3609,6 +3618,7 @@ body {
     assertConsoleErrorDev([
       "Hydration failed because the server rendered HTML didn't match the client.",
     ]);
+    jest.runAllTimers();
 
     expect(getMeaningfulChildren(document)).toEqual(
       <html>
@@ -5202,6 +5212,10 @@ body {
       </html>,
     );
     loadStylesheets();
+    // Let the styles flush and then flush the boundaries
+    await 0;
+    await 0;
+    jest.runAllTimers();
     assertLog([
       'load stylesheet: shell preinit/shell',
       'load stylesheet: shell/shell preinit',
diff --git a/packages/react-markup/src/ReactFizzConfigMarkup.js b/packages/react-markup/src/ReactFizzConfigMarkup.js
index 444952dc58502..800dd46e0ad77 100644
--- a/packages/react-markup/src/ReactFizzConfigMarkup.js
+++ b/packages/react-markup/src/ReactFizzConfigMarkup.js
@@ -224,6 +224,7 @@ export function writeCompletedRoot(
   destination: Destination,
   resumableState: ResumableState,
   renderState: RenderState,
+  isComplete: boolean,
 ): boolean {
   // Markup doesn't have any bootstrap scripts nor shell completions.
   return true;
diff --git a/packages/react-noop-renderer/src/ReactNoopServer.js b/packages/react-noop-renderer/src/ReactNoopServer.js
index fe00f28b0240f..119c9885db783 100644
--- a/packages/react-noop-renderer/src/ReactNoopServer.js
+++ b/packages/react-noop-renderer/src/ReactNoopServer.js
@@ -55,6 +55,7 @@ type Destination = {
   stack: Array<Segment | Instance | SuspenseInstance>,
 };
 
+type ResumableState = null;
 type RenderState = null;
 type HoistableState = null;
 type PreambleState = null;
@@ -153,7 +154,9 @@ const ReactNoopServer = ReactFizzServer({
 
   writeCompletedRoot(
     destination: Destination,
+    resumableState: ResumableState,
     renderState: RenderState,
+    isComplete: boolean,
   ): boolean {
     return true;
   },
diff --git a/packages/react-server/src/ReactFizzServer.js b/packages/react-server/src/ReactFizzServer.js
index f55d6f08043f4..65efe7c7e8935 100644
--- a/packages/react-server/src/ReactFizzServer.js
+++ b/packages/react-server/src/ReactFizzServer.js
@@ -5217,10 +5217,18 @@ function flushCompletedQueues(
       );
       flushSegment(request, destination, completedRootSegment, null);
       request.completedRootSegment = null;
+      const isComplete =
+        request.allPendingTasks === 0 &&
+        request.clientRenderedBoundaries.length === 0 &&
+        request.completedBoundaries.length === 0 &&
+        (request.trackedPostpones === null ||
+          (request.trackedPostpones.rootNodes.length === 0 &&
+            request.trackedPostpones.rootSlots === null));
       writeCompletedRoot(
         destination,
         request.resumableState,
         request.renderState,
+        isComplete,
       );
     }
 
@@ -5293,7 +5301,6 @@ function flushCompletedQueues(
   } finally {
     if (
       request.allPendingTasks === 0 &&
-      request.pingedTasks.length === 0 &&
       request.clientRenderedBoundaries.length === 0 &&
       request.completedBoundaries.length === 0
       // We don't need to check any partially completed segments because
diff --git a/scripts/rollup/generate-inline-fizz-runtime.js b/scripts/rollup/generate-inline-fizz-runtime.js
index ce613fdb8d039..3d097f63e216a 100644
--- a/scripts/rollup/generate-inline-fizz-runtime.js
+++ b/scripts/rollup/generate-inline-fizz-runtime.js
@@ -13,6 +13,10 @@ const inlineCodeStringsFilename =
   instructionDir + '/ReactDOMFizzInstructionSetInlineCodeStrings.js';
 
 const config = [
+  {
+    entry: 'ReactDOMFizzInlineShellTime.js',
+    exportName: 'markShellTime',
+  },
   {
     entry: 'ReactDOMFizzInlineClientRenderBoundary.js',
     exportName: 'clientRenderBoundary',
@@ -66,7 +70,7 @@ async function main() {
         });
       });
 
-      return `export const ${exportName} = ${JSON.stringify(code.trim())};`;
+      return `export const ${exportName} = ${JSON.stringify(code.trim().replace('\n', ''))};`;
     })
   );