The plant will start budding within two weeks of switching to a 12/12 schedule with the lights, however the plant may not be mature and thus wouldnt produce as much bud, when the nodes are offset that is a sign of maturity, that is a perfect time to start flower. It will work both ways its up to you when you start
If you use LST then the plant will not only start budding at a short height but can finish off at under 18 inches from soil top.
Another drawback to flowering early is the plant will not be able to support very much bud, and the stem could fold or snap under the weight. That vegetative time is the time for the plant to grow and become strong for the flowering cycle. If you want a quick harvest plant, go with the autoflowering dwarf strains.
Toastybiz is right too. I just read up on LST the other day, and it's ingenious. I think it's the very top stickie. Oh, question though. Can it make a dramatic difference in yield to LST? Or are all of the extra colas quite a bit smaller? Specifically would this make a difference if I was planning on doing SOG with some Lowryder 2. I need the most yield possible for approximately a 4x2 area.