How long do I have to add eggs to a laying broody hen?

[wild chick]

Thanks again, Egghead Jr. Too late now, but next time that's what I'll do. Also explains my last broody, sat 9 eggs, hatched 5 and left, even with one pipping. She refused that peeping egg and the other 3 that hadn't hatched. Those chicks are now 3 1/2 weeks old and they're doing great. I'll be happy if Gretchen hatches half of her clutch. I'll be moving her tomorrow to the privacy apartment.