Couldn't quite figure out how to phrase this question so it made sense. At this point, it's just hypothetical curiosity, but still I wonder... Chicken eggs take 3 weeks to hatch, correct? What if I have a hen that goes broody a week before I put fertile eggs in the nest for her to hatch? Will she continue to sit until the eggs have hatched (can she know how far they're developed?) - a total of 4 weeks - or will she get off a week early? What if it were two weeks difference between the time she started sitting and when eggs were placed in the nest (a total of 5 weeks sitting)??
It all depends on the hen. I've had some that are new to it and aren't really committed and get off the nest in 2 weeks. I have others that will sit for 2 months if they don't hatch anything.
Well, some of our hens believe that the ghosts of the golf balls they started on will hatch. We took the balls out the second time the broodiness happened, it took her a month to get over her broody mood the first time, with no golf balls the time doubled D: and now shes back at it and has taken two of our hens with her... Its a vicious cycle around here. I imagine it might depend a little on breed and the hen her self. Some are more persistent than others.