hey,
I hatch ducklings too,
you should probably research about 'internal pipping'
this is when the duckling has definitely broken through the air bubble and you can hear it chirping inside the egg. it is safe to make a 'view hole' once your duckling has internally pipped. A 'view hole' means that the duckling will have no risk of suffocating even if it's stuck in the egg. you make a 'view hole' at the big end of the egg (where the air pocket is) and it allows more air into the egg. The idea is that you are only letting air into the part where air normally is. You can find lots of information on view holes and internal pipping on the internet, or if you have any specific questions you can just ask me
Hope this helped!