Short answer is 2-3 weeks. Most breeders will wait 4 weeks after removing or changing roosters to be absolutely sure that any eggs they collect for hatching are from the rooster they want and not from the previous rooster. If you want her to hatch some eggs, then you can always buy fertile hatching eggs from someone who has a rooster and swap out the eggs she's sitting on for the ones you know are fertile.

Or, you can break her broodiness. There are several ways people choose to do this, probably the nicest way is to set her up in a wire bottom cage with food and water and no nesting material for a few days. Other people have reported success by placing ice packs under their hens or dunking their butts in a bucket of cold water.

This all depends if the roo had done his job and the hen you think is broody she makes the decistion to set not the roo when she feels there are enough eggs (clutch ) then she will be come broody.Anywhere between a week to 2 weeks If they are more than 7 days old they most likely wont hatch Embryos will begin to develop after the eggs are under a hen.so they can all hatch together.( If are fertilze)

maybe about 2 weeks after that

Well one way to tell take a flashlight to them and see if they are. That's one way to know if they are

I had a rooster that became aggressive, so I removed him from the coop 2.5 weeks ago. Now my hen is suddenly broody, and I know it is very likely that she is sitting on duds. My question: how many eggs/days/weeks after the last mating occurred are the eggs fertile? Hope that makes sense...