The 24-hour system originated in ancient Egypt. The ancient Egyptians divided the time between sunrise and sunset into 10 hours, plus 2 hours of dawn and dusk to form 12 hours of the day. Later, the Egyptians divided the night into 12 hours through a group of 12 stars, which is the source of modern 24 hours. Why is a day 24 hours? In ancient China, there were 'big time' and 'hour'. The big time is the hour, and the hour is half an hour, which is now an hour. Even if it doesn't take hours, since the Song Dynasty, the twelfth hour has been divided into twenty-four hours. For example, Zishi has been divided into Zichu and Zizheng.
The time corresponding to each hour before the Renaissance was not fixed. Until before and after the Renaissance, after the emergence of clocks and watches, the fixed time division began to popularize.
The rule of the 24-hour system is to divide the day from midnight to midnight into 24 hours, from the number 0 to 23 (24 is the midnight at the end of the day). This time recording system is the most commonly used in the world today. （YiTianWeiShenMeShi24XiaoShi）