Hi Chris and welcome to BYC We're so happy you've decided to join us
How consistent is your temp in the bator, are you using calibrated thermometers? If there are cold spots/hot spots in the bator you could have eggs at slightly different stages of development. Which means some may hatch early and others late. Just go with it and be patient. Ducks can grind on your nerves. They can take up to 48 hours after pip before they zip.