I’m not sure if what I’ve done helps, but here goes…
When a user hits a button to start a timer, I’m creating a record. One of those fields is ‘seconds remaining’. On creation I set this to:
(current date/time + 1500 seconds) - current date time : formatted as seconds
That is, it gets the value 1500 (which in seconds = 25 mins).
On creation of the record, I’m also setting a state to be Timer Started = Yes.
There’s then a workflow action that says:
Every 5 seconds (when Timer Started = Yes), update the record and set ‘seconds remaining’ = ‘seconds remaining’ minus 5
There’s also a Text element which simply displays Seconds Remaining.
It’s not perfect (it only updates every 5 seconds and the time remaining is displayed in seconds rather than mins:secs), but it works.