It is better to get the proper nutrients and use them at half strength. the time it takes to flood your tables is all the on time you need. Then drain. If you have hydroton in there you do that a couple times during lights on. If your watering the roots, no medimum, then as long as it takes for the roots to start to dry. Yes, go one hour down time to start but you dont want to go constant watering. You could run the airstone constantly or plug it into the timer too.