In hydro you can flower at 3-4 nodes and get 1-4 ounces per plant under a 600 watt HPS.

I say, 1-4 ounces, 'cause it depends on the number of major brances on the plant.

To be safe, you can flower just about anytime after puberty.... (seeing the first sign of hair) and as long as you have your plants dialed, no nutrient issues... they will do very very well... several ounces off little plants under 600+ watts of HPS.

good luck

SMB