Humans with any degree of compassion for animals tend to anthropomorphize them. They have no idea what a week means. They know to kinds of time...light time and dark time. They do not have the capability to think like a human even if we do think they do. Three ducklings, no matter how small they are, in what is essentially a foot square box is too many. If you think in terms of you being put in a small closet "just for a week" you might have an idea of what their experience will be. Depending on their age they may be better off being put outside now rather than having to endure the box. If they are not old enough to be outside then get a bigger cardboard box, cover the bottom with an old towel to absorb splashed water and droppings, change it at least once a day if not more often. Ducks grow pretty fast so that foot square cube is going to be really crowded really fast.