I have two Silkie chickens who just started sitting on some infertile eggs for the first time. This was about four or five days ago. I felt bad for stealing their eggs and didnt think they would be such good moms! I am going to go and get a dozen fertilized eggs on Sunday(two days from now), and swap them. Will my chickens know how long to sit on them considering they have already been sitting on the old eggs for four days(or by then almost a week)? Also how long do the eggs last for eating? Im guessing these ones are completly done for considering they have been kept quite warm.