diff --git a/packages/app/src/agent-stream/footer-spacing.test.ts b/packages/app/src/agent-stream/footer-spacing.test.ts
index f18d7ea27f..a2414fff5c 100644
--- a/packages/app/src/agent-stream/footer-spacing.test.ts
+++ b/packages/app/src/agent-stream/footer-spacing.test.ts
@@ -65,7 +65,6 @@ function timingFor(assistantId: string): Map<string, TurnTiming> {
     [
       assistantId,
       {
-        startedAt: new Date("2026-08-22T10:00:00.000Z"),
         completedAt: new Date("2026-08-22T10:00:02.000Z"),
         durationMs: 2_000,
       },
diff --git a/packages/app/src/agent-stream/layout.test.ts b/packages/app/src/agent-stream/layout.test.ts
index 9cc463590d..cfb379345d 100644
--- a/packages/app/src/agent-stream/layout.test.ts
+++ b/packages/app/src/agent-stream/layout.test.ts
@@ -73,7 +73,6 @@ function thought(id: string, seed: number): Extract<StreamItem, { kind: "thought
 
 function timingFor(...ids: string[]): Map<string, TurnTiming> {
   const timing = {
-    startedAt: timestamp(1),
     completedAt: timestamp(9),
     durationMs: 8000,
   };
diff --git a/packages/app/src/agent-stream/model.test.ts b/packages/app/src/agent-stream/model.test.ts
index 1aec54824a..d339acfe63 100644
--- a/packages/app/src/agent-stream/model.test.ts
+++ b/packages/app/src/agent-stream/model.test.ts
@@ -69,7 +69,6 @@ describe("buildAgentStreamRenderModel", () => {
 
     expect(model.turnTiming.byAssistantId.has("hidden-a")).toBe(false);
     expect(model.turnTiming.byAssistantId.get("visible-a")).toEqual({
-      startedAt: tail[2]?.timestamp,
       completedAt: tail[3]?.timestamp,
       durationMs: 1000,
     });
@@ -176,7 +175,6 @@ describe("buildAgentStreamRenderModel", () => {
 
     expect(model.turnTiming.runningStartedAt).toBe(null);
     expect(model.turnTiming.byAssistantId.get("live-a")).toEqual({
-      startedAt: tail[0]?.timestamp,
       completedAt: head[0]?.timestamp,
       durationMs: 3000,
     });
@@ -196,7 +194,6 @@ describe("buildAgentStreamRenderModel", () => {
 
     expect(model.segments.historyMounted.map((item) => item.id)).toEqual(["a1", "u1"]);
     expect(model.turnTiming.byAssistantId.get("a1")).toEqual({
-      startedAt: tail[0]?.timestamp,
       completedAt: tail[1]?.timestamp,
       durationMs: 3000,
     });
diff --git a/packages/app/src/agent-stream/turn-membership.test.ts b/packages/app/src/agent-stream/turn-membership.test.ts
index 171b9c060d..4483e4e1a7 100644
--- a/packages/app/src/agent-stream/turn-membership.test.ts
+++ b/packages/app/src/agent-stream/turn-membership.test.ts
@@ -86,7 +86,13 @@ describe("canonical turn membership", () => {
       assistant("heartbeat-2-reply", 6, "turn-3"),
     ];
 
-    expect(completedFooterIds(layoutFor(items, false).layout)).toEqual(["heartbeat-2-reply"]);
+    const completed = layoutFor(items, false);
+
+    expect(completedFooterIds(completed.layout)).toEqual(["heartbeat-2-reply"]);
+    expect(completed.layout.auxiliaryTurnFooter?.timing).toEqual({
+      completedAt: at(6),
+      durationMs: null,
+    });
   });
 
   it.each([
@@ -118,7 +124,6 @@ describe("canonical turn membership", () => {
     const completed = layoutFor(completedItems, false);
     expect(completedFooterIds(completed.layout)).toEqual(["done"]);
     expect(completed.model.turnTiming.byAssistantId.get("done")).toMatchObject({
-      startedAt: at(1),
       completedAt: at(9),
       durationMs: 8000,
     });
diff --git a/packages/app/src/components/message.tsx b/packages/app/src/components/message.tsx
index 54459ecda8..9ca8eaed10 100644
--- a/packages/app/src/components/message.tsx
+++ b/packages/app/src/components/message.tsx
@@ -578,7 +578,7 @@ export const UserMessage = memo(function UserMessage({
 interface AssistantTurnFooterProps {
   getContent: () => string;
   completedAt?: Date;
-  durationMs?: number;
+  durationMs?: number | null;
   onFork?: (target: AssistantForkTarget) => Promise<void> | void;
 }
 
@@ -616,9 +616,8 @@ const TIMESTAMP_REVEAL_MS = 3000;
 
 /**
  * Footer rendered next to the copy button at the end of an assistant turn.
- * Always shows the turn duration; swaps to the end timestamp on hover (web)
- * or tap (native). The hidden sizer keeps the label width stable while the
- * visible text swaps.
+ * Shows the turn duration and swaps to the end timestamp when both are known.
+ * A turn without a visible start shows its end timestamp directly.
  */
 export const AssistantTurnFooter = memo(function AssistantTurnFooter({
   getContent,
@@ -640,7 +639,10 @@ export const AssistantTurnFooter = memo(function AssistantTurnFooter({
   }, []);
 
   const durationLabel = useMemo(
-    () => (durationMs !== undefined ? `Worked for ${formatDuration(durationMs)}` : ""),
+    () =>
+      durationMs !== undefined && durationMs !== null
+        ? `Worked for ${formatDuration(durationMs)}`
+        : "",
     [durationMs],
   );
   const timestampLabel = useMemo(
@@ -648,7 +650,8 @@ export const AssistantTurnFooter = memo(function AssistantTurnFooter({
     [completedAt],
   );
 
-  const canSwap = Boolean(timestampLabel);
+  const primaryLabel = durationLabel || timestampLabel;
+  const canSwap = Boolean(durationLabel && timestampLabel);
   const showTimestamp = canSwap && (isWeb ? hovered : pressedReveal);
 
   const handleHoverIn = useCallback(() => setHovered(true), []);
@@ -679,22 +682,22 @@ export const AssistantTurnFooter = memo(function AssistantTurnFooter({
         containerStyle={assistantTurnFooterStylesheet.copyButton}
       />
       {canFork ? <AssistantForkMenu onFork={handleFork} /> : null}
-      {durationLabel ? (
+      {primaryLabel ? (
         <Pressable
           onPress={handlePress}
           onHoverIn={handleHoverIn}
           onHoverOut={handleHoverOut}
           accessibilityRole={canSwap ? "button" : undefined}
-          accessibilityLabel={canSwap ? `${durationLabel}, ended ${timestampLabel}` : durationLabel}
+          accessibilityLabel={canSwap ? `${durationLabel}, ended ${timestampLabel}` : primaryLabel}
         >
           <View style={assistantTurnFooterStylesheet.labelWrapper}>
             {/* Sizer reserves space for whichever label is longer so the
                 container width is stable across hover transitions. */}
             <Text style={assistantTurnFooterStylesheet.labelSizer} aria-hidden>
-              {durationLabel.length >= timestampLabel.length ? durationLabel : timestampLabel}
+              {primaryLabel.length >= timestampLabel.length ? primaryLabel : timestampLabel}
             </Text>
             <Text style={assistantTurnFooterStylesheet.labelOverlay}>
-              {showTimestamp ? timestampLabel : durationLabel}
+              {showTimestamp ? timestampLabel : primaryLabel}
             </Text>
           </View>
         </Pressable>
diff --git a/packages/app/src/timeline/turn-time.test.ts b/packages/app/src/timeline/turn-time.test.ts
index b5c13ee00c..35dacf397b 100644
--- a/packages/app/src/timeline/turn-time.test.ts
+++ b/packages/app/src/timeline/turn-time.test.ts
@@ -70,7 +70,6 @@ describe("deriveStreamTurnTiming", () => {
     });
 
     assert.deepEqual(timing.byAssistantId.get("a1"), {
-      startedAt: userAt,
       completedAt: assistantAt,
       durationMs: 7000,
     });
@@ -93,11 +92,37 @@ describe("deriveStreamTurnTiming", () => {
     });
 
     const expected = {
-      startedAt: userAt,
       completedAt: lastAssistantAt,
       durationMs: 7000,
     };
     assert.deepEqual(timing.byAssistantId.get("a1"), expected);
     assert.deepEqual(timing.byAssistantId.get("a2"), expected);
   });
+
+  it("preserves the completion timestamp when a canonical turn has no visible prompt", () => {
+    const firstTurnAt = new Date("2026-05-15T00:00:00.000Z");
+    const hiddenPromptTurnAt = new Date("2026-05-15T00:01:07.000Z");
+    const timing = deriveStreamTurnTiming({
+      isTurnActive: false,
+      activeTurnStartedAt: null,
+      tail: [
+        { ...user("u1", firstTurnAt), turnId: "turn-1" },
+        {
+          ...assistant("a1", new Date("2026-05-15T00:00:07.000Z")),
+          turnId: "turn-1",
+        },
+        {
+          ...assistant("hidden-prompt-a1", new Date("2026-05-15T00:01:03.000Z")),
+          turnId: "turn-2",
+        },
+        { ...assistant("hidden-prompt-a2", hiddenPromptTurnAt), turnId: "turn-2" },
+      ],
+      head: [],
+    });
+
+    assert.deepEqual(timing.byAssistantId.get("hidden-prompt-a2"), {
+      completedAt: hiddenPromptTurnAt,
+      durationMs: null,
+    });
+  });
 });
diff --git a/packages/app/src/timeline/turn-time.ts b/packages/app/src/timeline/turn-time.ts
index f090e7bfe2..4542962af4 100644
--- a/packages/app/src/timeline/turn-time.ts
+++ b/packages/app/src/timeline/turn-time.ts
@@ -2,9 +2,8 @@ import type { StreamItem } from "@/types/stream";
 import { startsNewTurn } from "@/agent-stream/turn-membership";
 
 export interface TurnTiming {
-  startedAt: Date;
   completedAt: Date;
-  durationMs: number;
+  durationMs: number | null;
 }
 
 export interface StreamTurnTiming {
@@ -25,13 +24,14 @@ export function deriveStreamTurnTiming(params: {
   let previousItem: StreamItem | null = null;
 
   const flushCompletedTurn = () => {
-    if (!currentUserAt || !currentLastItemAt || currentAssistantIds.length === 0) {
+    if (!currentLastItemAt || currentAssistantIds.length === 0) {
       return;
     }
     const timing: TurnTiming = {
-      startedAt: currentUserAt,
       completedAt: currentLastItemAt,
-      durationMs: Math.max(0, currentLastItemAt.getTime() - currentUserAt.getTime()),
+      durationMs: currentUserAt
+        ? Math.max(0, currentLastItemAt.getTime() - currentUserAt.getTime())
+        : null,
     };
     for (const id of currentAssistantIds) {
       byAssistantId.set(id, timing);
@@ -45,10 +45,6 @@ export function deriveStreamTurnTiming(params: {
       currentLastItemAt = null;
       currentAssistantIds = [];
     }
-    if (!currentUserAt) {
-      previousItem = item;
-      return;
-    }
     currentLastItemAt = item.timestamp;
     if (item.kind === "assistant_message") {
       currentAssistantIds.push(item.id);