Depends on a lot of things. The weather, especially your overnight lows. How draft-proof your coop is. Do you provide supplemental heat? How many are there. A few might get cold while a bunch can huddle for a little extra warmth. How predator proof is the coop? A rat, snake, or some weasels will kill chicks but will not harm a larger chicken. How well are they feathered out? Have you been lowering the temperature of the brooder so they get used to the cooler weather or keeping it really hot? Are there grown chickens in the coop that might kill young chicks?
I put my fully-enclosed brooder in the coop with a heat lamp and draft shield and keep them in the brooder until I think they do not need supplemental heat. With my first batch, that was at 4 weeks old in the middle of June. I then removed the brooder and left them locked in a pretty draft-proof at ground level coop for another month. I think they could have handled being in the run during the day, but my run is partially open on top and I was worried that they would have been very tempting targets for those hawks I have, being so small.
I'll do about the same thing again this year, but since I have adults in the coop now and I am a couple of months earlier in the year, I may wait a little longer to remove the supplemental heat or maybe leave the brooder with heat available to them with the brooder side door open a bit longer. My adults will go in tractors until the young ones are large enough to integrate.
Good luck!!!