1. What is happening (core idea) When you post a story: Instagram saves the time you posted it Then it has a rule: show only for 24 hours So it never "counts time" — it just compares times. 2. Like you're 5 years old Imagine: You put a sticker on a board at 10 AM The rule is: "remove it after 1 day" Now whenever someone looks at the board: If sticker is less than 1 day old → show it If older → don't show it Nobody is counting seconds. They just check the time. 3. Engineer-level (simple version) When story is uploaded: Server stores: created_at = time of upload When feed is requested: Server runs a filter: if (now - created_at < 24 hours) { return story; } So: 👉 Only fresh stories are returned 👉 Old stories are automatically ignored 4. Important clarification "The mobile app doesn't decide anything" Meaning: Your phone is NOT responsible for hiding stories Instagram server decides everything So even if you change your phone time → nothing changes 5. What is cleanup job?…