ThisShe'd need close to 20 days to accept the babies and even then some hens aren't good mothers. I have hens kill chicks as soon as they hatch, so they aren't allowed to hatch any.

Consider your hens breed- is it expected to be a good mother in general (silkie, orpington, etc) or unlikely.
Then there been enough time in the hens biologic clock to tell her chicks should be arriving? I would not put chicks or eggs soon to hatch under a hen who has been broody for less than 2 weeks. Her bio-clock may tell her something isn’t right- abandon the nest or eliminate the invaders.