You want to wait to flower for about a month, or until the plant has at least 4 or more nodes. If you switch the light cycle to early to 12/12 it can stress the plants and cause a higher male to female ratio, or induce hermaphrodites. Depending on the light cycle you have now, either 24/0 or 18/6, your plants should show preflowers...which would show up earlier in 18/6. It would be smartest to wait until you see the signs of preflowering before switching your light cycle. The more you let the plant veg the more bud you can potentially grow, but typically most people flower around 4 weeks of veg, which usually means about 5 weeks from when the plant first sprouts.