everything is lookin great, for pre sexing, they have to be at least 6 or 8 nodes i believe before you can tell anything, you have about 3, but this is a perfect time to switch to 12/12, they all seem healthy, so im sure your have a good female ratio, no probelms so far, so nothing to stress them into males. Basically, if you treat a plant good its whole life, most likely it will become a female.
You will need a Fig. 8 cord, not sure if they have them out there, looks like this
and plug that into an external timer, which you set the lights to 12/12, i think i posted that AG thread, should read thru it if you havent,
FIM is ok, but just top them, and put them into 12/12 in the next week or so, how much room you have to grow?
https://www.rollitup.org/advanced-marijuana-cultivation/151706-uncle-bens-topping-technique-get.html