question about flowering

[mysticheaven]

My plants are in wk1 of veg under a 250w metal halide 17/7 could i leave them for three wks, then put them under hps 250w 12/12 or is this to soon to flower they are fem jack hearer:stoned:

[Dutch Pimp]

4 weeks vegging is usually, fine. They should be about 10-15 inches tall by then....and mature enough to flower.