Once you've selected a variety, it's time to cook it. Sweet potatoes take less than 40 minutes in a 425-degree oven, but you may want to halve them for a more even roasting. Roasting wedges will take about 25 minutes. Whole sweet potatoes, meanwhile, take about 40 minutes. The cut side of the sweet potato will caramelize naturally. It also takes less time to roast a sweet potato than to peel it.