wait for preflowers at the very least.....

switching to 12/12 before preflowering can stress and lead to hermies/males.

even after preflowering showing definite sex can take a long time....but at the very least
wait for preflowers.....

you should start to see them at the 4th week of veg growth or about 6 weeks total time...but it can take longer....

patience my friend!