digital clock expression with a run time

[Colin Braley]

Search the archives and do an “Advanced Search” for something like “Clock expression.” This one has been asked a few times.
~Colin

[Mike Clasby]

Here is Dan’s Universal Answer, highly detailed, see notes at bottom to change, i.e. remove milliseconds.

https://www.motionscript.com/design-guide/up-down-clock.html

[Liran Tabib]

Instead of creating the Expressions yourself you can use these Digital Clock and Timer Presets:
https://www.vdodna.com/products/digital-clock-timer-presets/