my 2 cents. either get a simple timer with lots of tabs, or a simple timer with 15 min interval tabs already built in, or an expensive cycle timer.
my control unit runs on the second kind, fills/drains within 15 min, i fed them 6 times a day to start, then 5, then 4 during flower to end it. my unit has individual buckets, not a table, so everytime u fill for 15 min then drain, a 1/2" of water in the bottom of the pots can't drain back, so it gets sucked up eventually, acts like a buffer. if it didnt i'd feed them even more. during flower i did 1 fill soon after the lights are on, 1 more 2 h later, then again 2 h later, then 1 last fill/drain in the middle of the dark time, to make sure the roots didn't dry out
if u wanna use a cycle timer, i would go 15 min on, 1-3 h off. and have that timer plug into another cheap timer so it's only on when the lights are on for 18 h or 12 h. or don't. might not matter... trial and error