From what I have read, the only reason to use anything other than 24/0 during veg is to slow down the growth a bit, or because your ventilation/temps aren't good enough to run the lights 24 hours a day. As an experiment (I have two other smaller cabs too), I vegged once at 24/0 in one cab and 18/6 in another, and the 24/0 plants definitely grew faster...so I use 24/0 all the time now for veg. Whether you choose 24/0 or 18/6, stick to it. If you start at 24/0, stay with 24/0, so you don't increase your odds of hermies.

How long to veg for, well...that kinda depends on everything else: lighting, pot size, growth of the plants, strains, that stuff. But the idea is to train the plants under the screen until the screen has about one bud site per 4 square inches, then go to 12/12 and induce flowering. Then keep training the stuff under the screen while it's flowering, for the first 10 days or so of flowering, then let the buds pop through the screen, so that above the screen it is just buds.

That's 2 mil Mylar in there. I wanted to use flat white paint, but I had probs getting paint to stick to the laminate surface of the cabinet, so I went with Mylar. Mylar is a little more reflective than flat white paint (not much more), but paint seems like it'd be easier to deal with...if you can make the paint stick okay. I guess I could have taken a sander to the surface and roughed it up some to help it hold paint better, but I was lazy, and don't have a sander.