from the wood duck society.....
Predicting "Jump Day":
A hen wood duck usually lays one egg per day until her clutch is complete. The normal incubation period for a wood duck is usually 29 -30 days. You will have to get an accurate egg count and note the date sometime during the egg laying stage, before the hen starts her incubation. For instance, if you checked a vacated nest box some afternoon and found five eggs, and the date was April 10th, mark your calendar on the 10th with five eggs.In a few weeks, when the hen is incubating, you will need another egg count. Watch for the hen to leave for her morning or evening feeding, then re-check the nest box and get a total egg count. If the total egg count was twelve eggs, and knowing that during the egg laying process a hen usually lays one egg per day, add seven days [for the seven additional eggs] to the calendar you previously marked on April 10th. Using the new date of April 17th, you can add 30 days [incubation time] for the estimated hatch – which would be May 17th.
Now, due to the fact that wood duck hens will occasionally 'miss’ laying an egg on any given day during the egg laying process, the hatch date is just an estimate, but it will get you close. Near the hatch date, monitor the nest box more closely and re-check it when the hen leaves for her evening feed. On a day when you find some of the ducklings hatched- you will know that the entire brood will leave the following morning. At this point, avoid further contact with the ducklings or the hen. The hen and her brood will usually jump between 7:00 AM and 9:00 AM that following day, but the 'jump' can extend anytime up to noon –especially, if the hen feels threatened from predators or if the weather is inclement.