That can be pretty variable depending on if you have drains in the tanks or not. If no drains, then once a day for 30-60 seconds can be fine, depending on tank size. Just make sure to maintain air gap in false bottom.
Just a note, the timer that Mist King sells will allow many schedules. I use it so that I have a dry side of the week and a wet side of the week. The plants seem to like being soaked, then getting time to dry out a bit. Again, though, that's a lot of water and I have drains installed..