well if you wanna sex them early you should take a cutting of your plant, (i would wait til its on at least its4-5th node) then place the cutting inside on a 12/12 lighting schedule, within 8-10 days your plant should show its sex, if it has little balls then its a male and discard the cutting and the plant, if white hairs(pistils) show then congrats you have yourself a female. sexing your plant this way you don't disturb your plants vegging time. hope this helps ya a little!
LJ
GROW ON!