My RIR's were two weeks and my Red Stars were three weeks when we put them in their new coop that we got from ChickenSaloon.com. Only left the lamp on for a day or two before we took it out completely. Nice coop, but for the money, I wished I had built one now as the one I bought will be too small pretty soon. The website says it'll hold 10-15 chickens, but the nine babies I have in it now make me wonder what that's going to be like when they are full grown. I might just build a larger run for them since the coop will be plenty big for roosting at night. They absolutely love it and so do I! On the second day they put themselves to bed and have been doing it ever since. I go out in the morning just before I leave for work (615) and they are so happy to see us. Open the door and off they go. Sure wished I had done this a long time ago...