How to realize a generic "countdown X days until task" Thing?

[rossko57]

You might find this gives a starting point

Design Pattern : Expire Binding based Countdown timer

Problem Statement Sometimes you need to run a timer, but want to able to inspect the remaining time. This is not directly possible with either createTimer() or the Expire binding. Example - I have lighting-on timers that run for different duration depending on the trigger source or time of day. It is useful to have the timer behave “intelligently” - do not apply a new 5-minute request where there is still seven minutes of a previous trigger to run. But do apply it if there is only two minu…

I think for a daily countdown I would do decrement with rule, not expire.
But the design principle there of separating command from state you should find useful.

Obviously the counter Items would need persist/restore.