[Q]

despite previous poor results, I bought some ebay eggs and added some of my own that were due to hatch next tuesday.

One of the ebay ones has pipped and is cheeping away today - at least 3 days too early!

[HesterF]

It can vary slightly by incubator conditions and breed. When I hatched duck eggs last year, the Cayugas all pipped a couple of days before the Silver Appleyards and the breeder said they always found the Cayugas were earlier too. Also bantams have a shorter incubation time that large fowl.