dude, if your gals are in veg. you wanna shut down ALL lights for 24-36 hours. THen commence 12/12 after that. It really helps jumpstart bloomers. And makes most of 'em sex within a week.
I don't get what you mean with "after 12/12 do i just keep light on". Yeah, you run em 12/12 typically for 8 weeks dependent on strain & chop 'em.
you got a timer, or are you the timer (manual plug in & unplug?)
Yup that pretty much nailed it ! If u don't know flower time u can tell when the hairs are usually 3/4 amber