When do eggs 'pip'?

[Rorie]

My incubator instructions say that when the eggs pip, i should raise the humidity of my incubator. However, i am sure i read that i should raise it on day 18. Do they pip on day 18? If not, what is correct thing to do?

Thanks

 

[sunny & the 5 egg layers]

On day 18, raise the humidity and don't open the incubator at all. The eggs can pip anytime, from day 18 and up. It really depends on the hatch.