of course clone plants show pre-flowers, if not where the buds grow?
one plant grow from seed if you take one clone from that plant he growth like the mother and show pre-flowers male or female some times show both (hermophrodite). so you can wait until 4 or 5 weeks veg, and your plant show you pre-flowers. or you can force flower now and the plant show the sex, to do that put the plant on 12/12 cycle and he/she show up pre-flowers for sure.