Staggered hatching of duck eggs, incubated naturally?

We have a female welsh harlequin that was mated with a male mallard. Two of the ten eggs she was brooding hatched today, we have put some food and water in the house for them. She has stayed in the house sitting with the two ducklings and the remaining eggs. How long do we let her stay on the remaining eggs, will the ducklings be under stress staying inside? What is the normal thing to do in this situation?