Switching daylight after 1 week?

Right now I have my plants out sunrise roughly 630 sun sets around 7-8. What I wanna start doing is cutting down to 12/12 after a week of veg. I don't want them to get big could I do that? Or could I even start the 12/12 already? I really don't want anything big maybe about a foot of plant?

look into topping and lst. Even with 12/12 from seed you'd need height control to keep them under 1 ft. your not gonna get much off each plant but lst and topping will help.