The hen mallard will lay an egg a day until the clutch is complete at perhaps 8-10 eggs. Then she will begin to incubate the eggs for about 28-30 days. The eggs will all hatch on the same day, and as soon as the ducklings dry off, they will leave the nest with the hen and go to water nearby. They will not return to the nest. Please do nothing to try to help the mallards. They will do just fine one their own.