You have decide how tall you want them when they have finished, they doulbe maybe tripple in size when switching to flowering. Also what light you using, by the look of strobing on the pictures it is a hps which you can get good leave pertration but if you was using clf's you are better flowering early because the light does not penertrate as far down the plant. Hope that was helpfull, only a noob myself but have done a lot of reading.