Up your humidity to 85-90% and leave them be. None of my ducks took less than 48 hours from pip to zip, and I heard a lot of the same from others when I asked the first time. This seems to be pretty good advice, as the ones I've seen that pipped and died wouldn't have made it anyway- they may have pipped but there was a largely unabsorbed yolk and if I'd helped it would have been a disaster. I'm pretty sure they take longer because they are spending more time absorbing yolk.
If you can actually SEE the membrane is dry, you can wet the membrane with a q-tip and warm water, and leave wet paper towels inside the bator when you close it. If you leave a corner outside of the bator, wetting that will wet the entire paper towel eventually, so you won't need to open it again.
If you decide to help them, only create the zip line in the shell- leave the membrane intact and wet it thoroughly, then leave them to get themselves out of it. Helping them is quite a bit less harmful if they still have some work to do to hatch.