Whats the earliest you can start 12/12 on a sativa?

how do you keep a sativa dominant strain short enough to flower indoors?
Can you just start the 12/12 light cycle earlier than an indica dominant strain? did one grow but the plants got to tall, had to harvest early. Going to order some seeds, but I Figured I could play with what I got while i wait on my seed order.

i had a haze flowering at 6in. a sativa will flower and continue to grow, most people start buding at 10in