when can i start to tell sex

i wish i had picture to show yall, but its been about a month (they first germinated early december) and they have been growing really nice, i know how to tell them apart, just not sure when its suppose to happen.......does it happen when i put them on the 12/12 hour light cycle or do they do it on their own?

they start (as long as not auto) about 6-8 weeks cant tell really good without magnifying until about week 10-12 they dont need to be on 12/12 to presex they do that on their own... dont know of anyone being able to sex before week 6 without force flowering.... not suggesting it just passing along info.

thanks, exactly what i needed to know