Doughnuts are best 10 minutes after leaving the fryer. They are still good for a couple hours. After about 6 hours you'll notice the glaze (especially chocolate glaze) getting soft and starting to slide off the doughnut. This is the sticky finger phase of doughnut eating. read more
So I decided to do some research on How To Keep Your Doughnuts Fresher, Longer! Store Doughnuts in Ziploc Storage Bags or air-tight containers. This tip is good if you do, indeed, plan on eating the doughnuts the next morning (and the box has been opened). Place doughnuts in a Ziploc baggy or air-tight container. read more