can i go from 12/12 back to 18/6

i have 20ish plants that i want to know the sex. i am trying to establish some moms for later sog and dont want to waste time if they arent female. if i change the lights to 12/12 how long till i see "vaginas". also if i do this can i go back to vegging 18/6 with out fukn up my whole grow.

take a clone off each plant and number it with the same number on the plant it is from, then put the clones under a 12/12 cycle away from the other plants.
they will show sex while trying to root if you have a good cloning setup so you wont even need to change the mothers light cycle. just get rid of the ones whose clones are male.

cool i will try that how long does this usually take to see sex signs

i'd say about two weeks maybe more or less.....there's no specific timeline