My dominent hen stays with flock from day one. The others can have a week or so on their own, it's mainly for their own protection as I've had predator issues last month and the hen will take them right into the woods where predators lurk. I generally give them a good week until they can fly and run. I don't have any issues with them being in the flock as mama can and does keep track of them! How, I'll never know...I can't even count them all...but she does! My brooder opens to an outdoor pen, and inside to the coop. I will just leave the gate open and when the hen wants to she'll take them around, then she come back through the main door and nest in the usual spot. One hen I had would just look at the open gate and walk off, for weeks, I guess she liked being on vacation. I think alot depends on your flock too, if they aren't aggressive it will be fine. Some minor squabbles but they all seem to know exactly who belongs where.