Looking good, grouch. Sorry to hear about that fan falling. I had fans, lights, even shelves fall during my first grow...it sure can get messy. Good thing your plants escaped with only minor injuries.
Four to six weeks seems like the "normal" amount of vegging time for a grow on this scale. If you can't see any preflowers yet, I would recommend vegging a little longer and waiting for signs. Looks like you've got plenty of headroom for more growth (even accounting for the expected stretch early on in 12/12), so it couldn't hurt to let them get a little bigger before you switch the light schedule..
This might be a good time to think about taking some cuttings (if you haven't already). I like to take cuttings early enough that I get a second chance if the strain I'm working with turns out to be difficult to clone. Even if the parent plant turns out to be male, I can always toss the rooted male clone(s), and they don't take up much space (or require much light) while they're still rooting (which will likely take a couple of weeks). I always keep a tupperware tub and a low-wattage fluorescent fixture handy for cloning. I don't even always have a dedicated space for it...with CFLs heat really isn't an issue, so I've been able to root cuttings in a closet and a large cardboard box with no problems. And if stealth isn't a concern, that just makes it even easier.
Of course, if you've successfully cloned plants in the past, then you probably won't need any "practice"...and could wait until they start showing sex (either during veg or in 12/12). But if it's your first time, I'd recommend trying one or two out during veg just to see how it works out. That way, you'll still have another chance later on. Once your buds get past the 3-4 weeks of 12/12, you probly don't wanna be having to take any more cuttings.
