Mallard duck eggs typically take about 28 days to hatch after incubation begins. The female mallard lays one egg per day over about 12-13 days but does not start incubating until all eggs are laid, so embryo development and the actual incubation period start once the clutch is complete

. During incubation, the female sits on the eggs most of the day, leaving only briefly to feed. The eggs hatch together within about 12-24 hours of each other after roughly 28 days of incubation

. The hatching process itself can take some time. About 1-2 days before hatching, the duckling internally pips the air sac inside the egg to start breathing air. Then it gradually breaks through the shell over many hours

. In summary:

• Egg laying takes about 12-13 days (one egg per day).
• Incubation lasts about 28 days after the last egg is laid.
• Eggs hatch together within 12-24 hours.
• The actual emergence of ducklings from the shell can take a day or two once hatching starts

This 28-day incubation period is consistent across wild mallards and most domestic ducks derived from mallards