my first run in aero went with 15min on/ 45off, then i tried 30/30 and still nothing different. you can keep the sprayer off for atleast 45min during light cycle simply because your grow channels are full enclosed, the humidity in the channels will be like 99%, this moisture will be enough to keep roots from drying out between spray cycles. i believe the more important issue would be night time spraying, i used to run 15/90, if a spray cycle would give you root rot, it would be over watering at night time. look at your plants as a factory, once the lights go out, all internal mechanisms shut down, the roots will not suck up any water, they will just lay there and get wet, but since we have no media to hold onto moisture at night i sugguste you run a spray cycle a few times at night