The time of day when the body’s yin and cold are the heaviest is the Zi Hour. The daytime is yang and the nighttime is yin. Zi Shi refers to the time from 23:00 to 1:00 in the middle of the night, which is the time when the yin and yang reach the yin pole due to the waxing and waning of yin and yang, so it is the time when the yin and cold evil qi of the human body is the most vigorous. Yang energy needs to be protected at the time of Zi Hour. You should go to bed at night at the time of Zi Hour, maintain a good sleep condition and ensure sufficient sleep time are the best ways to nourish yang qi. The yin and yang of the human body will be affected in many ways depending on the time of day, the seasons, etc. The human body will combine with nature, and yin and yang can be used in many ways such as diagnosis of diseases, treatment, and health maintenance.