When to flower

I have 4 plants at 6 weeks old. They are from seed - top44 - and are now about 11" high and very bushy. I don't want them to get too tall but also don't want to reduce the yield. I'm currently on 18/6 with a 400w hps. What I would like to know is when should I be thinking of going to 12/12? Any assistance would be appreciated.

if they are about 11" right now, you can expect them to be about 30-36" if you were to flower them right now. they grow alot, I have a 400w HPS as well. if you don't want them too tall, I'd flower them now. I have about 6 ft to work with and still flower them at around 12" in order to have enough room.

I started 12/12 around 5 weeks and a foot tall, nice and bushy as well, so id say you're good to go.

Thanks for the advice - I'll switch now