I'm running an aero set up myself, and i put my system on a timer. I'm very new to all of this, however, my plants do seem to love their current treatment. 30 min on for every 2.5 hrs, 24 hrs a day. I also think it depends on whether you're res is in a separate compartment or in the same container as your plants, thus allowing the tips of their roots to gently sit in the solution when the pumps are not running, and preventing any drying out. I borrowed my method from "hatch", you may want to look up his threat titled "aeroponics hatch style", very informative. the last i read on him, he was also using a timed sequence. in my opinion, i think you should experiment with both methods, preferably side by side, and witness the results yourself. i plan on doing the same.