3 of my duck eggs took almost 48 hrs to zip with a little help from me. P.S. the 3 ducklings im refering to, hatched on day 31... I thought they were not going to make it, that is why I helped out a TINY bit. I just peeled away the shell where they had piped. Duck shells are sooo tough, I thought they were having a hard time breaking/zipping, so i helped a little. It worked out ok, they are here. actually country lovin has one of them.