Could they hatch today? Possibly but pretty unlikely. As OGM said, the 21 days for chicken eggs is more of a target than a strict scientific fact for each and every incubation. There are a lot of things that can affect exactly when an egg will hatch; heredity, humidity, how and how long it was stored before incubation started, and just basic differences in individual eggs. Bantam eggs, especially tiny ones like Seramas, tend to hatch early. The average incubation temperature has a big effect, if it is too warm they tend to be early or too cool and they tend to be late. I’ve had eggs hatch two full days early in an incubator and under a broody hen. I’ve had them hatch on time with broodies and that same incubator on the same settings. I’ve had all eggs hatch in less than 24 hours after the first one hatched. I’ve had hatches drag on for three days, incubator and broody.
I’ve had chicks come completely out of the shell within an hour of external pip. I’ve had chicks wait over 24 hours from external pip until they are out of the egg. They are just not consistent at all. It can make it pretty nerve wracking.
Good luck!
