Just did a quick check in on them. All are internally pipped now, a couple are tapping away inside, a couple are just breathing inside... must be resting and exercising those lungs. Coming up on 24 hours since the first one internally pipped, but I have no idea when to make a safety hole because I don't know when that exact 24 hr mark is - I only know it was sometime between 3pm and 8pm that it pipped inside yesterday... just keep waiting? Any signs I should be looking for - like if it's getting tired or gasping in the air cell?
Personally I wouldn't rush them. If they are in the air cell, they should be able to knock the shell out easily.
Storey's Guide to Raising Ducks says "Ducklings require 24 to 48 hours to completely rim the shell and exit".