glad to hear that the lost chick was found.
maybe like you were thinking that she make it like that to keep they warm, as i said, she know the best. i never disturb or watch over my hen when she is broody (that's almost 3 years ago). i always let her take care of them, i know she can. hen...
many people said, 15-30 minutes.
as for me, i never worry about it since i know that the hen know much better about keeping her eggs than me.
trust her (i suggest).
especially with *village chicken* here, they're best mother.