I write the date the eggs were laid on the egg then i count 21 days past the lay date so if the egg doesnt hatch on its due date I give it a day or two and if it still doesnt hatch i know its bad.
I hope you're not trying to use your broody hen as an incubator. Generally speaking, a broody hen is really only equipped to complete one broody cycle which would typically last between 21 and 23 days, if you keep putting more eggs under her and removing chicks as they hatch just to keep her brooding, that would not be a good idea. Keeping her brooding for an extended period of time would probably be very stressful and unhealthy for her. I generally would never set an egg on the same day as it was laid either. I have always believed that the egg needs to thoroughly cool for at least 24 hours before starting incubation, whether it be a broody hen or incubator. I usually wait 2 to 3 days before setting eggs. I feel that when the egg is laid, it's already heated up and it needs to cool before it gets incubated to start development. If you think about it, a clutch of 12 eggs would have at least 10 eggs that have been cool for more than 2 days and some up to 10 days. I don't know if an egg set the same day it was laid would develop or not, but that's just my thoughts.