I put mine into the coop (in a wire dog carrier or a separate apartment) between 3-4 weeks if the weather is good. I'll put them up at night back into the brooder if necessary for protection. Usually between 4-6 weeks I let them loose with the flock. Mine have lots of room so they can get away from any of the mean ones. I found anything later than 6 weeks to be difficult, by then the cockerels are thumping chests and generally can get into trouble with the alpha male, if I have one in with the rest of the flock.
I'm getting ready to separate any day now. I've got 6 cockerels (I think) varying in age from 5 weeks to 8 weeks. They are in with the main flock now, but I'm preparing to move them to their own pen. I was hoping to be able to sex the chicks in the brooder (2 weeks old) before moving the boys so that I could move them all at the same time but I don't know if I'll be able to wait another 3-4 weeks. We'll see how long I can wait.