I've seen a surprising amount of predators about during the day. My neighbor locked his ducks up at night and let them forage in his yard during the day. He had 3 ducks for a month. Maybe you have less predators where you live.
I bet my spunkiest duck could jump/fly over a 2 foot fence if I tempted her with mealworms.
I trained my ducks to go to bed at night on request for mealworms. But I have a close relationship with them. They are pets and eat out if my hand.
I don't give them food in their barn room because then I would have to give them water as well and they would make a big wet mess. If they weren't pets I would gently herd them to bed. And then gently throw some mealworms at them after they go in. They would probably eventually get the point and go to bed more willingly.
If you do get ducks again and find that they aren't the right choice for you please find them a new home. Releasing them on a pond is unkind as they need someone to protect and feed them.