Need to know if i should start to flower...

I recently topped my 3 week old plant...about a week ago. And it's just starting to sprout the two main future colas...is it too early to start flowering, or should I let the two little sprouts get a little bigger? I have limited space for my single plant grow so I don't want to let it get too much bigger...any input greatly appreciated!!

is this the advanced MJ cultivation room why the hell do you ask a newbie question.............lol

If you don't want to get tall, put them on the 12 hour day. Three weeks is plenty of time for the seedling to get ready. You don't say what strain these are. If they are sativa dominant, by all means switch to 12 hour. Indica dominant I might veg a little longer as they will stay relatively short anyway.