In the Chinese Calendar, the time has neither beginning, nor end. It's in eternal inchanging cycle. Or we can consider that the time is a kind of eternal circle. This concept corresponds exactly to the theory of the Confucianism, which says that the supreme task of a living is to perpetuate the life, for a human being, a supplemental task is imposed, this is to honor his acenstors, implying to surpass his parents, in conducts, in realization. What do humans, bees, ants, plants, ...
To quantify the time both abstract and imperceptible, the scientists of the Emperor, often the calendary officers of the Son of the Sky, invented a system of Sexagesimal dating. ie, the Ganzhi system 干支纪年法.
To do this, The Sky has been divided first into 10 stems, called TianGan (天干) and then the Earth into 12 branches, called DiZhi (地支), each represented by a symbol animal, and also called Chinese Zodiac Animal:
The combination of the columns TianGan et DiZhi gives 60 exhaustive possibilities. Each combination is a GanZhi, abbreviation of TianGan et DiZhi. These 60 Ganzhi are the Fundamental of the Chinese Zodiac and of the Chinese Astrology.
Each Ganzhi is the name of a year, and each 60 years form a full cycle: it begins by the first year JiaZi (甲子), and ends by the last year GuiHai (癸亥).
We remark that each Ganzhi year is associated with an animal, so in the Chinese Zodiac, the same animal returns at each 12 years.
At each 60 years, the cycle restarts and remains in space and time...
As reference, a remarkable JiaZi (甲子) year is the year 4 AC in the Gregorian Calendar.