Is it normal for 1 egg to hatch a week later?

[Chickadee-23]

I had 9 bantam eggs that my hen was sitting on i had to put them incubator after 10 days of her sitting on them cause mother was killed by raccoon, anyways 5 hatched on May 5 & 1 hatched on May 11 and 3 were not fertile so my question is it normal for the one egg hatch later like that? And why didnt it hatch on the day it was due May 5?
Thanks

 

[sourland]

My guess would be that the late hatching egg was added to the clutch by another hen 6 days after the hen started setting.

 

[donrae]

My guess would be that the late hatching egg was added to the clutch by another hen 6 days after the hen started setting.

This.

I always mark the eggs I'm wanting momma to hatch so I can pull out added bonus eggs while she's brooding. Other hens seem very generous about donating eggs to her, or some broodies literally go steal them!