In ancient China, 2 hours was regarded as one hour, and one day and night was *** 12 hour. The night time is called night shift, and there are five hours in the evening. A watch: 19-2 1 min; Second look: 2 1-23 points; Night shift: 23- 1 min; Fourth watch: 1-3 points; Even number: 3-5 o'clock.
Yan Zhenqing, a great calligrapher in the Tang Dynasty, said in his poems, "This is the night for men to study. Black hair doesn't know how to study early, and Bai Shoufang regrets studying late. "