20 minutes. According to the inquiry of Bright Life. Com, yam bean is small, 15 minutes can be cooked, while yam bean is big, it takes 25 minutes to cook. If you cook in a pressure cooker, the time will be shortened, and the time for cooking yam bean will not be too long. For 20 minutes, you can observe the state of yam bean during cooking. When it becomes soft and waxy, you can turn off the fire and let it cool naturally.