I know I REALLY want them to be nice to each other!! we had a few unseasonably warm days late last month and I let everyone free range together and they seemed to do well. I was thinking about putting the littles out during the day in a dog crate so they can all see each other and spend some time together. But if they’ve been in the house (which we keep at about 60 because we have big dogs who get hot

) can they just go out for the whole day?
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It would probably depend on current temps. If they are only used to 60 degrees but its 15 outside, then maybe a couple hours then keep increasing. If its above freezing then they can go out longer. Do you have a garage they could try for a couple nights that might have in between temps? If they are huddled in a dog crate together they will fluff up and keep each other warm. However I'm no expert and there may be better advice on here how to acclimate. I actually had my 2 week old chicks in a dog crate outside with their "heating pad mama" when it was around freezing and they did great. They stayed out most of time and ran back underneath when needed so chickens are more hearty than you might think. Your birds are fully feathered so they will acclimate well. The first time I left my first batch of chicks without heat (8 weeks and freezing) I thought I would wake up to dead chicks and they were running around all happy the next day.
Another note, when I integrated my birds older with younger, I actually stood in their coop and watched them roost together for the first time (I know, I know, crazy, but I was curious about their process) They definitely had a pecking order which is normal, but one just beat the crap out of the younger ones to the point there was blood and she just wouldn't stop after so many days, so I ended up getting rid of that one, it was so brutal. They say dont put human emotions into their pecking order, I agree, but I just couldn't handle the blood and wanted to protect the rest. I think I just had a really mean chicken! Not all are like that. Hopefully you have nice ones!
Anyway, back to your original post, haha, your chickens are designed to handle cold, cold temps. They should do well.