I'm a noob but I can help a bit...I think. Like DTRave420 said, wait until your plants are 1/2 the height you want them to finish at. If you are using cfl's, I wouldn't let them get too much bigger because the light penatration won't be very good. If you are going to switch to HPS or MV...then I would let them go for a bit. The plants look good so far. Keep up the good work.