I have brought in the late hatchers several times. They spend a day or two inside, being fed yogurt+baby scratch "soup" from a dropper. I keep it warm and covered. We put uncooked rice in a baggie and nuke it. Then put a towel on it, and make alittle nest. The baby settles into the warm rice bed and covered with a towel, and it usually drifts off to sleep and is quiet. The rice stays warm for several hours. When the babies get stronger, they start pecking at the chick starter and walking well, I put them back in with the group.
Last summer I had a momma hen with around a dozen chicks and one hatched out late. She ignored it. I brought it inside, fed it, kept it warm, etc. Little thing cheeped its head off night and day. After a few days, this little one seemed stronger, and I put it back w/ group at night. It ran in and got under momma. She killed it that night. Really hard lesson. I'm guessing momma knew something wasn't right.