Traditionally, Chinese people used a zodiac 12-hour system to tell the time. The 24 hours of a day were divided into 12 shichen 时辰 [a two-hour period], with each zodiac animal representing a shichen. Besides, the 12 zodiac animals correspond to the 12 dizhi 地支 [earthly branches]: zishu 子鼠 [rat], chouniu 丑牛 [ox], yinhu 寅虎 [tiger], maotu 卯兔 [rabbit], chenlong 辰龍 [dragon], sishe 巳蛇 [snake], wuma 午馬 [horse], weiyang 未羊 [goat], shenhou 申猴 [monkey], youji 酉雞 [rooster], xugou 戌狗 [dog], haizhu亥豬 [pig] (all in the form of Earthly Branch + Zodiac Animal). When referring to a shichen, instead of directly using the name of a zodiac animal, people often used the earthly branch corresponding to the zodiac animal, for example, youshi 酉時 instead of jishi 雞時. The first shichen, the hours of the rat, starts from 11 PM and ends at 1 AM. And the hour of the ox is the period from 1 AM to 3 AM, and so on.
See also https://zh.wikipedia.org/wiki/%E6%97%B6%E8%BE%B0.
