Cook on low for 6 to 7 hours, or on high for 3 1/2 to 4 hours.
Test the sweet potatoes by carefully removing the largest one from the slow cooker and inserting a fork to the center of the potato. A perfectly cooked potato will have little to no resistance. If the fork doesn’t go in smoothly, cook for thirty minutes more and then recheck. Larger sweet potatoes may need up to an hour of additional cooking time.