Hey buddy. Now the thing with flowering is really up to you. You can start to flower a lone if you choose to do so. One question that you want to ask your self in deciding if it time to flower is height. How big do you want those bitches to grow. Once the transition has taking place you can expect those girlz double maybe even triple in size. So really it is up to you. Couple of questions that will help you out a little more too.
Are they sativas or indicas, Because sativas grow so tall indoors.
How much space do you have from floor to the top of your light?
Are you wanting a big harvest or just a harvest, because if you want a big harvest then you should veg longer but only if you have enough room height wise to grow?
Anyway good luck.
Solarphlare