I've done both successfully. Putting day old chicks under the hen while she is in her nest at night works the best for me. Day old chicks out of the incubator will be young enough for her to bond to their chirping if her own chicks are the same age or it's close to 21 days and it is apparent all her eggs have hatched. Everybody wakes up in the morning as one big happy family. It's a problem if your trying to crowd too many chicks under a hen with a full nest of eggs. And with older chicks and this doesn't work so well. She won't recognize their voices and will usually fail to accept them. Timing is every thing. Night time is the best time to try.Broody question.....I've gone back and read about placing a different chicks eggs under a broody and sometimes they will accept it. ???? If you put day old baby chicks under her would she accept them or just eggs??