Mine, here in south Ga. have been in coop and run for a week. But now we are having cooler weather and high winds. They are 6 weeks old. Today's high is 19 below average of 70. It got down to 34 last night. So the heat lamp is on for them. It's easy to be over protective of the little babies. Even though they aren't little anymore.
That will make them very happy. By the way I was talking about myself being over protective. LOL I let mine out for a while this morning, but now the wind is blowing very hard and its about 45 so I put them back in their coop. Daddy doesn't want any sick chick's!
Those cute little chicks that follow their mother into your yard after being out in the woods for a week or two didn't have constant heat 24/7 and they do just fine. Of course they have mom to run to when they get cold. A good heat lamp for them to sleep under and run to during the day is all they need. And you have to be their mother by making sure they get under it at night rather than lost in some corner. Outside on day one has always worked for me. This may not be such a good idea if you only have a couple of chicks. But we all have different situations.