You bake sweet potatoes in the oven for about forty five to sixty minutes at four hundred degrees Fahrenheit until they are completely tender. Smaller sweet potatoes may finish cooking in forty minutes, while larger tubers can require up to seventy minutes. You can test for doneness by inserting a fork into the thickest part of the potato to ensure it slides in easily. Allowing the baked potatoes to rest for five minutes before cutting improves their texture.