Healthy chick hatched on day 17??

[Chick-az-ee]

This is my first time incubating eggs and I bought some eggs from a local breeder on craigslist. I started counting from the exact hour I put them in, and at the beginning of day 17 one chick pipped and about 8 hours later it hatched and has been fine since. I didn't know it was possible. One more hatched on 19th but didn't make it, and today is day 20 and have 1 starting to pip, I think the rest will hatch by 21. What do you think could have caused such and early hatch? incubator temp too high? Or could the egg have some how been pre incubated before I received it? They were warm when i got them. Any ideas?

 

[sourland]

Day 17 is really early. I have had bantam eggs hatch on day 19+. Very possible that egg may have been incubated prior to your receipt of it.