That is what I was wondering about. I read somewhere ( not sure where) that they have a mysterious way of controlling the hatch because hens don't lay all their eggs the same day. I was figuring that I might be able to remove the eggs and add them to the incubator for the last few days if I need to. I will candle them before hand. Given the fertility rate I would be lucky to get one!I've never added eggs over multiple days. I place them all at the same time so they can incubate equally. Otherwise you can have a rather stressed out mother hen trying to hatch eggs and tend to hatched chicks simultaneously until she decides to abandon remaining eggs in favor of protecting the chicks that are already hatched.
How is your weather these days???