What is the longest a duck should sit on eggs before The eggs hatch?

[TXGal49]

My Silver Appleyard mama Duck has been sitting for 30 days from my calculation.
Can you tell when eggs are about to hatch?
Mama has carried out 3 or 4 empty egg shells away from the nest in the last 2 or 3 weeks. They are not bloody nor have any smell to them.
A Pekin has been trying to nest next to the mama but I have been taking away these eggs.
Mama takes food and bath breaks of about 15 to 20 minutes about twice a day.
Any thoughts about these issues would be greatly Appreciated.

 

[Isaac 0]

Go out there at night, and take a bright flashlight and shine it under the egg. Tell us what you see. 30 days on the nest, her eggs are most likely infertile or rotten if they haven't hatched yet.