Ducklings can go without food and water for up to 3 days post hatch as they still have the remains of the yolk to sustain them. A lone baby in a brooder is not a happy baby, so leave him with his siblings, even if they are taking their time. Once he has a buddy they can go in the brooder together.
It's great to hear more are making moves to hatch. In most of my hatches there seems to be an early bird, then the rest hatch a bit later more as a group.
