Don't panic, I read a fascinating article on hatching duck e g g s, I wish I saved the link. It said the usual progression was that the duckling would internally pip, then eventually externally pip, then the duckling rests for about 12-36 hours before zipping. I noticed most of my eggs took two day from pip to out. Also, my ducks didn't 'zip' like all my chickens have, they basically took off the whole top of the shell and then eventually kind of shimmied out of the opening. all my e g g shells were one big piece and then a bunch of tiny pieces (as opposed to my chick hatchings where I got two halves of e g g per chick. Hope this helps!
Oh, and I also noticed that at least my ducks hatched much more quietly and with less rocking. I don't know if that is the norm, but I rarely heard them peeping and the e g g s didn't rock and roll like when the chicks hatched.
