diff --git a/sa/type-converter.go b/sa/type-converter.go
index 2ffb5bc1bc10..d7d92eb79422 100644
--- a/sa/type-converter.go
+++ b/sa/type-converter.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"time"
 
 	"github.com/go-jose/go-jose/v4"
 
@@ -35,6 +36,18 @@ func (tc BoulderTypeConverter) ToDb(val interface{}) (interface{}, error) {
 		return string(t), nil
 	case core.OCSPStatus:
 		return string(t), nil
+	// Time types get truncated to the nearest second. Given our DB schema,
+	// only seconds are stored anyhow. Avoiding sending queries with sub-second
+	// precision may help the query planner avoid pathological cases when
+	// querying against indexes on time fields (#5437).
+	case time.Time:
+		return t.Truncate(time.Second), nil
+	case *time.Time:
+		if t == nil {
+			return nil, nil
+		}
+		newT := t.Truncate(time.Second)
+		return &newT, nil
 	default:
 		return val, nil
 	}
diff --git a/sa/type-converter_test.go b/sa/type-converter_test.go
index c0849e759e27..8ca7d35d1994 100644
--- a/sa/type-converter_test.go
+++ b/sa/type-converter_test.go
@@ -3,6 +3,7 @@ package sa
 import (
 	"encoding/json"
 	"testing"
+	"time"
 
 	"github.com/letsencrypt/boulder/core"
 	"github.com/letsencrypt/boulder/identifier"
@@ -151,3 +152,26 @@ func TestStringSlice(t *testing.T) {
 	test.AssertNotError(t, err, "failed to scanner.Binder")
 	test.AssertMarshaledEquals(t, au, out)
 }
+
+func TestTimeTruncate(t *testing.T) {
+	tc := BoulderTypeConverter{}
+	preciseTime := time.Date(2024, 06, 20, 00, 00, 00, 999999999, time.UTC)
+	dbTime, err := tc.ToDb(preciseTime)
+	test.AssertNotError(t, err, "Could not ToDb")
+	dbTimeT, ok := dbTime.(time.Time)
+	test.Assert(t, ok, "Could not convert dbTime to time.Time")
+	test.Assert(t, dbTimeT.Nanosecond() == 0, "Nanosecond not truncated")
+
+	dbTimePtr, err := tc.ToDb(&preciseTime)
+	test.AssertNotError(t, err, "Could not ToDb")
+	dbTimePtrT, ok := dbTimePtr.(*time.Time)
+	test.Assert(t, ok, "Could not convert dbTimePtr to *time.Time")
+	test.Assert(t, dbTimePtrT.Nanosecond() == 0, "Nanosecond not truncated")
+
+	var dbTimePtrNil *time.Time
+	shouldBeNil, err := tc.ToDb(dbTimePtrNil)
+	test.AssertNotError(t, err, "Could not ToDb")
+	if shouldBeNil != nil {
+		t.Errorf("Expected nil, got %v", shouldBeNil)
+	}
+}