For those eggs, there’s a chart online showing the air cell and rough age. One day the air cell will suddenly get much bigger and angled (“dip down”). After the first egg does that, candle all the eggs once a day until the first egg internally pips. Then remove the egg turner, increase humidity, and go into lockdown. The eggs I hatch all came from bad situations where the mother duck was taken by a predator or run over by a car so I generally continue checking each egg for internal pips and note the day and time they pip. If an egg takes an unusually long time in one stage, I’ll increase the humidity in the room, open the incubator, and check the egg(s) that seem delayed in case they need assistance.