My ducks free range during the day, and are locked up tight in a small duck house to protect them from predators every night without fail. Just because of the way my life works, my schedule with them is very consistent-- I let them out in the morning at 8 am, and lock them up when the sun goes down (whenever that is, according to season).
During laying season, when I go to let them out in the morning, I invariably find that the girls have already laid their eggs. I don't know exactly when, but anyone who is going to lay is definitely done by 8 am and ready to go on about their day when I let them out-- they let me hear about it if I'm even a minute late! Once out, they don't come anywhere near the house until sundown.
You could certainly try to set up a nest box near their shelter for your duck hen to lay in during the day, but at least in my experience, you're more likely to find that she lays her eggs before you even let her out in the morning.
Good luck with your ducks, and have fun with them!