they may have a little transplant shock when doing it during 12/12 but it shouldnt affect them much, but it is probably ideal to do your last transplant before switching to 12/12.
not sure if you put them in 12/12 to sex and then switched back to a veg cyle, will often slow them down for weeks as they revert back to a veg state.
most plants will show their sex usually when they are 4-7 weeks old so you do not have to put them into 12/12 to sex them.