I wouldn't recommend it either. It's a experiment for me. I didn't veg at all. 12/12 under my 1000w hps since day one. They are all bagseed so no idea on flowering times. But however long they need, I'm not in any hurry. I was more or less testing different trimming/prunning/growing methods to discover which one give most yield and potency. 12/12 from seed was a attempt to rush the experiment.
So my next grow will benefit greatly from this one. But, like I said, It's not really worth it to 12/12 from seed. It's fast yes, but with a extra 2-3 weeks of veg, you'll still have short plants but it will greatly increase your yeild.
If vertical feet is what your lacking in. Consider a SCROG. You can cram a lot of vertical growth under the screen. Plus your canopy would have a predetermined height; Which helps a lot.
I was told 12/12 from seed would produce naturally a single cola only plant. But it doesn't I assure you. You must trim for that. I did most in that fashion. But a few have different variables. Some were supercropped, topped, low branches trimmed, top branches trimmed, some were tied. Damn near everything. You really can shape these things to a damn pretzel shape if you want to.
Basically, it boils down to this: What kind of harvest are you happy with? What kind of budz do you want? I like main cola budz the most. Always more potent in my opinion. I'd seriously advise some veg time to assure your not disappointed with your harvest. If you just want a quick harvest, look into cloning, and a perpetual harvest may be for you.
Don't let me discourage you though. If you wanna try it go for it. But SOG grows are best with a suitable strain and lots of plants. That's the whole point of a SOG. Less per plant, but a lot more plants. If you do 12/12 from seed it's essentially a SOG hopefully. Deffinitly don't rush one plant. That would be pointless. I could only see it being worthwhile if you had over 15 or so. Good luck all, stay safe!
-Dude'r