It means you backup window is 2 hours!!
but if you wanted it to be longer and your resolution was 15 minutes the next available window would be 2hrs 15 minutes, then 2hrs 30mins, then 2hrs 45mins.
If your resolution was 30 minutes it would go 2hrs 30, 3hrs
If your resolution was 10 minutes it would go 2hrs 10, 2hrs 20, 2hrs 30
A time would come when it will be 24 hours?