update doc

flutter/lib/src/sentry_flutter_options.dart

@@ -272,11 +272,11 @@ class SentryFlutterOptions extends SentryOptions {
   /// for every [ISentrySpan].
   ///
   /// When enabled, the following metrics are reported for each span:
-  /// - Slow frames: The number of frames that exceeded a specified threshold for frame duration.
-  /// - Frozen frames: The number of frames that took an unusually long time to render, indicating a potential freeze or hang.
+  /// - Slow frames: The number of frames that exceeded the expected frame duration. For most devices this will be around 16ms
+  /// - Frozen frames: The number of frames that took more than 700ms to render, indicating a potential freeze or hang.
   /// - Total frames count: The total number of frames rendered during the span.
   /// - Frames delay: The delayed frame render duration of all frames.
-
+  ///
   /// Read more about frames tracking here: https://develop.sentry.dev/sdk/performance/frames-delay/
   ///
   /// Defaults to `true`