O.K. I work on this time frame: It takes on average 24 hours from internal pip to external pip (which is sort-of where you are now), then it takes, again, on average, 24 hours before the duckling starts zipping the shell and eventually completes the hatch. Now you've got an (artificial) external pip and the duckling can breathe, which is all it needs now. Wait another 24 hours (or longer) and see if it creates another pip hole so it can start zipping. If it doesn't you can start assisting, but it will be better to give him plenty time to attempt hatching by itself first. I know it's nerve wrecking and it can feel like they're never going to hatch, but be patient and relax. You are doing great!
What's happening with the rest of the eggs?