how long does it take to bake a yam
1 Turn the oven on to 425. 2  Bake for 45 minutes for sweet potatoes/yams that are 2-3 inches in diameter. 3  For sweet potatoes that are up to 4 inches in diameter, bake for an hour. 4  For super large sweet potatoes, bake for an hour and 15 minutes.5  After the time has elapsed, don't open the oven but turn it off. For sweet potatoes that are up to 4 inches in diameter, bake for an hour. 2  For super large sweet potatoes, bake for an hour and 15 minutes. 3  After the time has elapsed, don't open the oven but turn it off. 4  Let the sweet potatoes sit in the oven for at least 30 minutes but up to an hour.