diff --git a/app/api/exercises/[id]/session/advance/route.ts b/app/api/exercises/[id]/session/advance/route.ts
index 3802e5d..7abb45d 100644
--- a/app/api/exercises/[id]/session/advance/route.ts
+++ b/app/api/exercises/[id]/session/advance/route.ts
@@ -43,6 +43,12 @@ export async function POST(
     return NextResponse.json({ error: 'Session closed' }, { status: 410 });
   }
 
+  // Mark session as started on first interaction
+  await sql`
+    UPDATE sessions SET started_at = now()
+    WHERE id = ${row.id} AND started_at IS NULL
+  `;
+
   const currentIndex: number = row.current_question_index as number;
   const questionCount: number = row.question_count as number;
 
diff --git a/app/api/exercises/[id]/session/route.ts b/app/api/exercises/[id]/session/route.ts
index 76d3fa9..740da03 100644
--- a/app/api/exercises/[id]/session/route.ts
+++ b/app/api/exercises/[id]/session/route.ts
@@ -54,7 +54,7 @@ export async function GET(
       SELECT
         ${exerciseId},
         ${userId},
-        now(),
+        NULL,
         0,
         e.end_time,
         e.duration_limit
diff --git a/app/api/submissions/[sessionId]/autosave/route.ts b/app/api/submissions/[sessionId]/autosave/route.ts
index ea6e780..7e47a4a 100644
--- a/app/api/submissions/[sessionId]/autosave/route.ts
+++ b/app/api/submissions/[sessionId]/autosave/route.ts
@@ -75,6 +75,12 @@ export async function POST(
     );
   }
 
+  // Mark session as started on first interaction
+  await sql`
+    UPDATE sessions SET started_at = now()
+    WHERE id = ${sessionId} AND started_at IS NULL
+  `;
+
   // Upsert the submission
   const upserted = await sql`
     INSERT INTO submissions (session_id, question_index, response_text, submitted_at, status)