you wont no if its not a boy til you see pre flowers if you get balls you no its a boy it wont be to long till you no normly to weeks to pre flowers aper
We haven't used Mercury lights for growing only MH and CFL but as far as the flowering stage goes it can take anywhere from a couple of days to 2 weeks to show sex. Just when you think nothing is gonna happen either pistals or balls appear. You have 1 more week left before you even need to start worrying, keep it on 12/12 and just be patient. We go a little crazy waiting for them to bud to but this current grow we used clones so we new they would eventually bud lol Good luck, we hope they are females!!!