Ap Dijksterhuis in Psychological Science Agenda:
When you are facing an important decision, others will sometimes tell you to postpone your decision and “sleep on it” first. In my case it was often my grandmother who gave me this advice. It is a belief many people intuitively share: It helps to put a problem aside for some time in order to arrive at a better decision. Somehow, waiting seems to help us to differentiate between the vital and the futile. Postponing a decision helps us to base our decisions on the appropriate reasons.
But does this “folk belief” hold in a scientific experiment?