My little buff orpington broody (who went broody at the tender age of just 5 months old) hatched her babies on September 25 and 26'th.
She was a great broody and a great mother, teaching her three hatchlings all the things baby chicks need to know, and keeping them toasty warm in their early weeks.
We wanted to make it easier for her to rejoin her own cohort group, so in addition to putting her and her hatchlings in a large dog pen inside the hen house with the other chickens, we also began letting her out of the cage about an hour a day to re-socialize with her cohort group, beginning when the hatchlings were about 3 weeks old. (We had a heat lamp to help keep the hatchlings warm while Mom was out playing with the older birds).
Then, only 27 days after the first baby hatched, Momma rushed out the cage when I released her for her hour of playtime, and she ran into the nesting box the way that we humans do when we have GOT to go to the bathroom. She plopped herself on that nest box as quick as her little legs could take her there, and so I let the other chickens out into the yard for play time and let her sit alone in the nest box.
Next thing I know, she's coming out of the nest box and there is a warm egg where she sat.
I noticed after that, I had to force her into that cage to take care of the babies, so at day 29, I figured she must be finished with her role as momma. Now she lives 24/7 with her cohort group, and the babies still live in the dog cage inside the bigger birds coop, with a heat lamp to keep them warm at nights.
And it seems to be working out just fine.
I guess my momma bird knew exactly when it was time to move on, even before I knew.