I have little hatching experience but I know ducks can take more than a day from internal to external pip and more waiting after that to actual hatch. The hatch days can vary depending on heat in Bator as well.
What was the date you set them? What breed are they? What temperature has your incubator been?
Sorry for the barrage of questions but those answers might help us figure out what is going on. Make sure your humidity is now up to around 70%, because otherwise they might become shrink wrapped. They can take 24 to 48 hours to finish absorbing everything after external pip and start to zip, so they may not hatch for a day or two yet.
I set these eggs Saturday may 6
These will be a mixed breed of rouen/pekin or rouen/alesbury
Temp has been 99.5-100.5
How can I get the humidity up I put water in and the humidity raised a little but not enough I heard that u was supposed to open one of the vent plugs for the hatch is this true?