I agree with most everything that NorEastFla is saying, although I have a couple of points. Yes the drain cycle does draw in fresh air with every cycle, but does not add dissolved oxygen to the water itself. And the way I see it, you just cant get to much oxygen to the roots. So I like to get it there every way I can, including using air pumps (in the water) and hydrogen peroxide. But is it necessary, no not really especially if it's not hot.
The long on/off times is largely based on the setup itself (including the growing media). For moisture retention I like using Coco chips, it holds moisture more than twice as long as the hydroton (
grow rocks). I don't really have any set flood/drain times myself. I just watch the plants and
growing medium, and adjust as I feel necessary. But I don't think that I have ever had luck with off times longer than 30 min. The timer I used (for the flood and drain systems) has minimum 30 min on/off times, and with 1 hour off the plants tend to wilt (especially in warm weather). In fact during hot days I often set the timer for "30 off" and "1 hr on" during the hot part of the day (especially while getting direct sunlight). In the late afternoon when they get shade, I'll set it back to 30 on/off.
But in a
drip system (using coco chips and 5 gallon buckets) I have often used a 30 on and 2 to 2 and 1/2 hr off, even on hot days. In fact there has been a few of times where ether the gfi tripped or I forgot to plug the
pump back in, and did not even find out until 3 or 4 pm the next day, and the plants still were not wilting. It really all depends on the setup, so I try not to give people the on/off times they should use. But rather give starting options, and stress keeping an eye on the plants for them to decide what works best for there setup.