I'm not sure what you are powdering them with. That might make a difference. I once asked an Ag professor that keeps chickens if Sevin made the eggs unsafe to eat. He said no, they are safe. I'd assume the same for the unhatched chicks. However, the eggs are porous so the developing chick can breathe. I'd dust the chicken and the nest, but not the eggs directly. It is not so much that I would worry about the Sevin injuring the chick as worrying that the powder blocks the pores on the egg shell.
Again, I don't know what you are using so take that into consideration.
I don't do ducks. I'd think it would be the same, but I'm not 100% sure.
By the way, I don't eat the eggs on the day that I treat, no matter what he said. I'm just weird that way. But the next day, I don't worry about it.
Editted to add: I would definitely treat before they hatch, partly for the health of the chicks but also for the health of the broody. That same Ag professor said that roost mites kill more broodies than anything else.