How old is too old to stick under broody

[The Prairie]

Have a hen setting 9 eggs due mid this week. I also have a friend hatching some chicks I've been wanting today. I would like to stuff a couple under momma when the others hatch and see if she'll take them but they'll be 4 to 5 days old by then. How old is too old to stick hatched chicks under a broody with day old chicks?

 

[chickenlittle21]

As long as the chicks are less than a week old, like the chicks your getting, they should be fine to stick under a broody.