Since when in History did men count days of 24 hours?

Question

Since when in History did men count days of 24 hours?

Answer 1

The current sexagesimal system of time measurement dates to approximately 2000 BC, in Sumer. The Ancient Egyptians divided the day into two 12-hour periods and used large obelisks to track the movement of the Sun. They also developed water clocks, which were probably first used in the Precinct of Amun-Re, and later outside Egypt as well; they were employed often by the Ancient Greeks, who called them clepsydrae. The Shang Dynasty is believed to have used the outflow water clock around the same time; the clocks were introduced from Mesopotamia, possibly as early as 2000 BC. Other ancient timekeeping devices include the candle clock, used in China, Japan, England, and Iraq; the timestick, used in India and Tibet, as well as some parts of Europe; and the hourglass, which functioned similarly to a water clock.