As long as you have the space for them to grow, then you can keep them in veg as long as you like. Mine have been in veg for about 5 weeks and I just put them in 12/12, they looked just like yours at the same age and now they're about 8-14 inches tall and 8-16 inches wide.

Some of the bad things that can happen with overcrowding, especially with hydro where you have water evaporating all the time, is mold. Where a few leaves are bunched up and there's no airflow between them, it starts to get all wet in there. It looks like they're sweating. This can very quickly lead to mold and other bad stuff. Once you get mold in a bud you are in big trouble and must perform surgery on your plant. I've never had it happen myself, so I don't feel I have the experience to tell you how close is too close. Also the amount of air you've got circulating makes a big difference.



There are two things to remember when putting your plants into flowering.

1)They will double or triple in height by the time you're done. First they'll slow down growth and start getting less blades per leaf, then they'll start shooting up pretty fast.

2)It is best to wait until the plants are sexually mature before flowering them, even though you can do it beforehand this may lead to hermies/mutations. Sexually mature means waiting until the branches start alternating like stairs instead of looking like a ladder, which should be happening in a couple of weeks at the rate you're growing. (it also depends on what type of light you're getting to them, alot of reddish light is believed to cause plants to begin this transformation earlier.

I don't think you have anything to worry about as long as you're prepared to make room if needed. Just be ready for them to get alot bigger is all I'm saying. Good luck, I'll be watching.

__________________
Burning down the house since 1981.

My First Indoor Grow!