I'm not sure exacly how to spot preflower?

How old are they?
2 1/2 months

Or, you could leave your plants 18/6, take clones, and put the clones 12/12 to know their sex.
Lack of space was the problem!

I will be done with sexing in 1 week (4 weeks in total ) and I hope I dont get hermie because of the long flowering period to spot female under fluos. I will put them under a 24/0 light cycle for 3 to 5 days to force them back into VEG and then 18/6 for 2 to 3 weeks before I start cloning.

Any advice ?