I put mine out at 3 weeks old and it was in 20s and 30s overnight and 50s +/- during the day. They did just fine, but I had heat lamps available to them and they were completely shielded from the wind (back and side of the cage are closed in and I hung a think blanket over the front overnight).
So, to clarify, heat lamps are on 24/7, during the day - front is open, at night - blanket goes over the front.
I couldn't wait to get them out of the house because the last week inside (week 2 of their life) they got to be SO stinky and poop cleaning got realy old, so they had to go out. Since they went outside (heat lamp 24/7) - they started laying eggs at 5.5 weeks old; must be happy enough