diff --git a/packages/client/ui-trajectory/src/client/TrajectoryTimeline.tsx b/packages/client/ui-trajectory/src/client/TrajectoryTimeline.tsx
index 0bf7e9b6db..8ad1afefc1 100644
--- a/packages/client/ui-trajectory/src/client/TrajectoryTimeline.tsx
+++ b/packages/client/ui-trajectory/src/client/TrajectoryTimeline.tsx
@@ -7,6 +7,7 @@ import {
 import type { TrajectoryTurnModel } from './layout.ts'
 import {
   deriveTrajectoryTimeline,
+  formatTimelineOffset,
   type TrajectoryTimelineMode,
   type TrajectoryTimeRange,
 } from './timeline.ts'
@@ -81,6 +82,18 @@ export const TrajectoryTimeline = memo(function TrajectoryTimeline({
   onRecordFocus,
 }: TrajectoryTimelineProps) {
   const model = useMemo(() => deriveTrajectoryTimeline(turns, mode), [mode, turns])
+  const durationByIndex = useMemo(
+    () => new Map(turns.flatMap(turn =>
+      turn.groups.flatMap(group =>
+        group.cells.flatMap(cell =>
+          cell.timeSeconds === null || !Number.isFinite(cell.timeSeconds)
+            ? []
+            : [[cell.index, Math.max(0, cell.timeSeconds * 1_000)] as const],
+        ),
+      ),
+    )),
+    [turns],
+  )
   const dragRef = useRef<{ pointerId: number; anchor: number; width: number } | null>(null)
   const [draft, setDraft] = useState<FractionRange | null>(null)
   const [hover, setHover] = useState<number | null>(null)
@@ -324,6 +337,7 @@ export const TrajectoryTimeline = memo(function TrajectoryTimeline({
               .map((span) => {
                 const left = (span.start - domainStart) / domainDuration
                 const width = (span.end - span.start) / domainDuration
+                const durationMs = durationByIndex.get(span.index)
                 return (
                   <span
                     className={css.span}
@@ -339,7 +353,9 @@ export const TrajectoryTimeline = memo(function TrajectoryTimeline({
                         ? 'true'
                         : 'false'}
                     key={span.index}
-                    title={span.label}
+                    title={durationMs === undefined
+                      ? span.label
+                      : `${span.label} · ${formatTimelineOffset(durationMs)}`}
                     style={{
                       '--trajectory-span-left': `${left * 100}%`,
                       '--trajectory-span-width': `${Math.max(width * 100, 0.35)}%`,
diff --git a/packages/client/ui-trajectory/src/client/timeline.ts b/packages/client/ui-trajectory/src/client/timeline.ts
index 26c297f110..2e2227df39 100644
--- a/packages/client/ui-trajectory/src/client/timeline.ts
+++ b/packages/client/ui-trajectory/src/client/timeline.ts
@@ -32,6 +32,17 @@ export interface TrajectoryTimelineModel extends TrajectoryTimeRange {
   turnBoundaries: readonly TrajectoryTimelineTurnBoundary[]
 }
 
+/**
+ * Format a timeline duration with a compact unit.
+ * @param milliseconds - Non-negative duration in milliseconds.
+ * @returns Millisecond or second label.
+ */
+export function formatTimelineOffset(milliseconds: number): string {
+  if (milliseconds < 1_000) return `${Math.round(milliseconds)} ms`
+  const seconds = milliseconds / 1_000
+  return seconds >= 10 ? `${Math.round(seconds)} s` : `${seconds.toFixed(1)} s`
+}
+
 function laneFor(kind: TrajectoryCellKind): number {
   if (kind === 'tool' || kind === 'subtool') return 2
   if (kind === 'message' || kind === 'compacted') return 1