How to change the delay time value on a button push?

[JOHI]

There is an post where I present a timer object
that encapsulates millis() completely. This makes the approach more simple.

Use multiple millis

If you are using multiple timers, then my millisDelay class simplifies things by keeping all the variables and running/stopped flags in the class. see How to write Timers and Delays in Arduino You should combine that with a task base approach to your sketch to avoid the 'delay' mentioned above. see my tutorial Multi-tasking in Arduino [multitaskingDiagramSmall]