As usual there are almost as many different opinions on growing as there are growers. Some info says you can flower a plant from around 6 inches with 4 nodes, while others say the plant needs to be in pre-flowering before you switch to 12/12. Yet, a plant that is vegging at 6" isn't going to be in pre-flower? I grew my Indica plants to around 16" on the window ledge, then put them under lights in a 12/12 cycle. They've been there for 2 weeks and seem to be beginning flowering, but was this the right way to do it? How would I make a small plant go into pre-flower? Should I have done this first? Thoughts?
I don't think I've ever waited for them to preflower. I just let them get to whatever size I want and do the flip to 12/12. I just wait for them to show their sex after the flip.
I remember reading somewhere that you can start a plant off in 12/12 lighting and it will flower right away. Of course this means that the plant will not be very tall or produce very much bud at all, but it can be done. What I do is wait until the plant is approximately half the total height I want it to be, then I switch to 12/12. It really all depends on how big you want the plant and how much bud you are looking to harvest. Want a big plant that produces a lot of bud? Keep it on 24/0 or 18/6 cycles for a while , and be patient. On the other hand, if you are okay with a small plant that produces a small amount of bud, switch it to 12/12. Like you said, there are as many different opinions as there are growers, so just find what fits you best when it comes to size and run with it.