I have 6 chicks (2 silkies, 2 BRs, 1 EE, and 1 RIR) that will be 8 weeks tomorrow. I live on the Eastern Shore of VA, and they've been outside since Christmas Day, so about 1.5 weeks. The thing I was real careful about was lowering their temperatures. The brooder temperatures would only go down to 50 degrees. So the last two weeks they were inside I took them on excursions to the coop (with about a 40 degree temperature). I started with only an hour or so, and just a few days before they went outside they were out in the coop for most of the day (5-7 hrs). Therefore before they went out they were used to 40 degree days and 50 degree nights.
The first few nights they were out in the coop I got lucky with temperatures. We had two straight days of 50 degree highs and 40 degree lows. Then I lowered to 40 and 30. And finally the last 3 days have been 30 and 20. I check on them probably more than I need to. I chalk that up to these being my first chicks. But they always seem fine, except when I wake them up. Haha! They snuggle together at night, like they've always done. But I've never seen them huddle, even early in the morning when it's the coldest.
So just make sure you're careful about acclimating them to temperatures and I think you'll be just fine.
If they've had the light for a few days out in the coop, and you slowly wean them off it I think they'll be ok. Just make sure to keep it on hand just in case.
Now if you have older birds in your coop, that's a whole different ball game.
