Time to flower? Big Bud, NL, White Widow

Should I start the flowering stage? Its going on eight weeks since seedlings, I have four plants in this picture, the biggest one is a big bud, behind it (which you cant see in the picture) is a white widow as well as the one in the front right, then in the back right is a NL, all femenized btw. All are different hieghts as you can see, but from the top of the bigbud I only have about 1.5 - 2 feet left of vertical space. Under a 1000w HPS, how much more you think they will grow once flowering, double? tripple? any suggestions?

its gonna work out nice. ur gonna have some big bitches. im guessing a lb or more but im no pro.

Don't know if it's true or not, but i would think that waiting until they show naturally before the 12/12 cycle, will improve thc levels. Mine are just short of three mo's old and i just moved them yesterday.