Timer until variable changed?

Question

PHP

Who knows how to make a timer that will count down the time until the variable changes?
The variable is incremented every 3 days by the same number. On the 1st of each month, the variable is reset to its initial value and starts incrementing again.
I've already broken my head

Answer 1

you store in basis value of a variable, and date of the following change. On the
backend, you get the variable itself, the date of the next change, and the current time of the server .