im not sure what some of you dont understand about taking a clone from plants that you have grown from seed, and then sexing the clone to determine the sex of the seed you planted.. come on.
as far as sexing goes.. i like to root my clones with 20-4 light schedule. if i want to quickly determine the sex of the clone, i will take my light schedule down by one hour a day, untill i reach 12-12. once i reach 12-12 my plants show sex in 3-6 days depending on the strain. i have tried going from my regular veg cycle to a week of 8-16 and then back up to 12-12 because i was told that it would make my flowers show earlier. doing it that way always took the 10-14 days that a normal switch to 12-12 would have given me.