I'm bored, so long answer
Most people don't use flood with coco. Too messy. You will clog your drain, pollute your reservoir, and over water your coco. But if that won't stop ya: You'll want to flood when your plants have dropped a good chunk of the water in their containers. Best way to tell? Pick em up. They are heavy after watering, considerably lighter when thirsty.
Flood tables generally should run to max fill. You don't wanna cut that short. You'll never keep a set flood level unless you lower drain valve to the height desired. That is, you can't really control your flood time to set flood height level: the medium absorption rate will vary (alot) and change over time, not to mention dissipation variables.
Young coco plants might need watering every 3-5 days. Mature plants usually want a daily feed- more if your pots are smallish. So.. Check weekly to adjust your schedule. It's possible to flood coco, no doubt. But the problems exceed the positives imo.
A far better plan would be to either switch your medium to hydroton/clay, or switch your feeding method. They sell drip emitters that actually convert your drain tables into drip feeders. Drip on coco is best. Coco kept consistently moist and breathing creates wondercrops equivalent only to what I've only ever seen done with black gold soil.
For coco Make sure you have some thrip/mini fly deterrant. -They like that wet top.
I use flood and drain and hydroton. I've used coco, it yields better but it's simply too much cost, work, waste and issues. (those smallflys and coco.. ugh).
Hydroton: MUCH fewer problems though. Cleaner, cheaper, reusable (with rinse and ph shock).
For Hydroton: I water about ever 5 hours. Used to be 4 with HPS. (Considerably less dryout with 10 degree cooler temps using LEDs however. (flowering @ 77f). And yes, water at night: we're not feeding, just making sure hydroton never dries out. CAP variable/intermittent timers are your friend.
