Who knows about domestic ducks hatching their own eggs?

I have a pair of ducks that are about 1 year old, I think). My female Welsh Harlequin built a nest and now has 7 eggs in it. She seems to sit on it at night but will get off when I get home from work when she wants to be fed. She doesn't usually go right back on the nest. I'm not sure if she's staying on the nest all day long or not. I know that they won't actually start incubating the eggs until they are done laying, but if she's sitting on it at night, but not all day, will the eggs start to develop and then not hatch? I guess I'm just not sure how the whole process works as I've never had a duck build a nest and be "broody." My ducks are just pets, but it would be fun to hatch some ducklings.