how much water?

hey, i'm about to start plumbing up my growing cupboard. I'm going to have 2 plants in the cupboard with drippers delivering the water from my reservoir (via a pump ofcourse) and then draining back. My medium is cocoa. and my question is how often and for how long should i water for? because the timers that i can find either don't have enough programs for 1 day or the minimum time they can be on is 15 minutes.

thanks