It depends on the size of the sweet potatoes and the temperature of the grill or smoker. In general, you can plan on the following times for medium size potatoes: - 250 degrees F. - 2 to 2.5 hours - 300 degrees F. - 1.5 to 2 hours - 350 degrees F. - 1 to 1.5 hours - 400 degrees F. - 45 minutes to 1 hour