How to add countdown timer for each row?

I am developing an app that keeps track of how much time a user needs to sit.
like a user made an entry timer will start (countdown timer/Reverse timer ),i.e I will add 20 minutes timer for a user so it will show a live countdown for users that continues.
thanks in advance

Live countdowns are not possible, as they would require continuous formula recalculation, which Appsheet does not do. The closest you can get is to put your countdown expression into a virtual column. It will update the countdown every time you sync the app, or make a change to that record.