Welcome to 7Forums!
With those options, you can set how much time windows will take an action after you are not taking any action
So if you set 3 minutes for turning off the screen or going to sleep and leave it alone it will scedule these action after 3 minutes.
I don't really understand the part where you explain that the timer stopps. I do not
recommend setting the same values for both options under 'on battery' or 'plugged in' state.
I would just increase the 'on battery' / sleep time to 5 or 10 minutes and see if it works.