Is it OK to let your broody work overtime?

[MrRoy]

I have 5 good banty eggs in a homemade bator(12 days today). I have a broody hatching 6 today&tomorrow. After my broody hatches all her current clutch, would it work out to take the chicks away and place the banty eggs under her for the remaining 9 days or will she leave the nest once the chicks are gone? Or is this putting too much stress on her?

 

[Mahonri]

Once chicks hatch under her, she's done.

Also, it's not healthy for them to go over a month. Some actually die setting on eggs.