This should first talk about the role of yam. Yam is sweet and flat, and enters the lung, spleen and kidney meridians; Not dry or greasy; Has the effects of invigorating spleen and lung, invigorating stomach and kidney, strengthening kidney and essence, improving hearing and eyesight, helping five internal organs, strengthening bones and muscles, calming nerves, and prolonging life. Therefore, if we use yam to tonify the spleen and stomach, it is best to use it at the fourth hour (9: 00 am to 1 1); If you consider the use of strengthening kidney and benefiting essence, it is best to use it at unitary time (that is, from 5 pm to 7 pm); If it is used for chronic cough due to lung deficiency, it is best to use it at Yinshi (3 am to 5 am). This is inferred from the meridian flow of traditional Chinese medicine. You can refer to it appropriately and don't be too rigid.