Queso45 said:If you're worried about height you might want to consider switching to an 18/6 light cycle. Its been said that the plants growth is less stretchy and has closer node length.
I recently transplanted my plants about 3 weeks after the 1st one showed pre-flowers (I was still vegging though). I've just read that it can stress the plant if you transplant it too far into flowering.
Just my 2 cents...
Good luck with your first grow.
It will be as stressful as you make it, obviously you are taking your chances, the deeper into flower you get, but if you do it nicely, the plants should not even flinch. Compared to the possible stress to teh plant from becoming rootbound, I would easily prefer some minor stress, from a later transplant