How is the timer on Activity?

Question

Android

I have several Activities
AND one main Activity
When nothing happens on the rest, then after some time, the program should start the main Activity
How can I implement this?
Tell me please. Maybe something to read?
I'm just new to this topic

Answer 1

Firstly, in Android, something happens only on one activity that is currently on the screen. Nothing should happen to the rest.
Secondly, launching some kind of activity without an explicit user action is bad manners.
Thirdly, in most cases, in a modern application, several activities are not needed. One fragment is enough.