i believe it is 30 days from the start.
so say you start botting april 1st, and use up all your hours by april 18th, you will have to wait until atleast may 1st, where you will start gaining your hours back that you used up to that limit. so say you botted 20 hours a day, you would receive 20 hours back may first, 20 hours back may 2nd and so on up to your maximum. so by may 3rd if you havent botted, you would have 60 hours available again to use