You shouldn't see much in the last few days as the chicks are taking up almost all of the available room in the egg. It is almost all dark, except for the air sac. Given that you don't know how old the eggs are but candling indicates they are mostly done, I might give it 3-5 days in an incubator under lock down conditions.
ETA: Lockdown conditions mean no opening the brooder, no candling, high humidity (60-65%) You can't control what happened when the broody got off the nest but you can control the conditions from this point on in your incubator. You will do more harm than good at this point by opening and closing the incubator and candling. The humidity needs to stay high in order to have good hatches. Speaking from experience.