What's the best age to butcher a duck?
When do ducks start laying?
How successful are nesting boxes?
Will ducks breed and brood in the fall?
As with all living things, there can be multiple answers. Depending on the breed and size, ducks can be butchered anywhere from two months on...
Most start laying in the 5-7 month range and they always made nests on the floor (corner) of their coop. They don't seem to want to hop up and use a nesting box.
While ducks might breed in the fall, they probably wouldn't brood. It seems many breeds no longer go broody, but if you want fall babies you could probably use an incubator.