Countdown Timer API use cases

Seven worked examples, each with the code, the timer type it needs, and the failure mode that catches people building it the first time. These are written for the case where a deadline is a fact about a record rather than a decoration on a page — where something has to happen at zero whether or not anyone is watching.

Which timer type each one needs

The choice of timer type is the decision that shapes everything else, and it follows from one question: what is the deadline anchored to?

Use case	Timer type	Because the deadline is…
Flash sale	fixed	the same instant for every customer
Product launch	fixed	a date on the calendar
Auction close	fixed	shared, and movable by anti-snipe rules
Webinar	fixed or recurring	a scheduled start, once or weekly
Cart reservation	duration	elapsed time from checkout, and pausable
Booking hold	duration	elapsed time from selection, and extendable
Trial expiry	personalized	different for every customer

If two rows sound right for your problem, you probably want two timers. A launch that also runs a per-customer discount window is a fixed countdown plus a personalized one — not one timer trying to be both.

All seven

Flash sale deadlineOne deadline, many surfaces, and a server that decides when the price changes.Cart reservationHold stock for fifteen minutes, pause during payment, release on a webhook.Trial expiryA per-customer deadline that agrees with your billing, in-app and in email.Auction countdownA shared clock every bidder sees identically, with anti-snipe extensions.Webinar countdownA recurring schedule, reminder ladders, and a room that opens on time.Product launchOne timer driving the landing page, the email, and the release itself.Booking hold expiryA seat held for ten minutes, released automatically when nobody confirms.

What they all have in common

Different problems, but the same four moves. If you are building something not listed here, this is the shape to copy.

Create the timer with the record

One POST, with an Idempotency-Key derived from the record ID so a retry cannot produce two deadlines. Store the returned timer ID against your own row.

Attach a rule per moment you care about

One for the deadline, and usually one or two before it. Rules are unlimited on every plan, so a reminder ladder costs nothing beyond the requests to create it.

Make the handler safe to run twice

Delivery is at-least-once. Deduplicate on the event ID, and check your own current state before acting — a paid order should not be cancelled by a delivery already in flight.

Enforce server-side at the decision point

The countdown on screen is presentation. When the deadline gates money or inventory, read the status endpoint rather than trusting what the browser submitted.

For the consumer-facing versions of these ideas — pomodoro timers, classroom clocks, event countdowns built without code — see the main CountdownShare use cases.

Every example runs in Sandbox

Free with any account and no plan needed. Set a two-minute duration instead of two weeks and watch the whole flow in a single sitting.

Create an account Read the quick start