ok so my buddy has a couple plants that have been in 12/12 for 13 days now and only 2 of them have shown their sex. Their being grown with a bunch of high power cfls. Im wondering if the male that was discovered after 4 days may have contaminated them.
a male would not prevent the others from showing sex. how old were the plants when he put them into 12/12. They won't show sex until they are mature enough... which may be your problem but i'm not sure how old they were when they were started at 12/12 If there are any significant light leaks that can be confusing for the plants and may also delay the showing of sex. 13 days is a bit long for them not to show sex (depending on their age) -- but all you can do is wait. is it possible that they are showing sex, but you're not identifying their often hard to see female pistils?
I would at least wait until they have alternateing nodes. This usualy shows that a plant has reached maturity and is ready for flowering, topping, cloneing or anything else you are ready to do with it. You CAN flower a plant whenever you are ready but generaly i usualy like to wait until i see that to flower. Genetics also play a big role in how long it takes plants to actually show sex when they are flowering, it also determines how long the process of flowering takes. How long have the plants been on 12/12? If its more then a couple weeks like the thread title states i wouldnt risk a hermi throwing them back into veg.