Mythical history

What is the calendar-making in early China?

This transformation happened not because scientists discovered the laws of celestial motions. Mathematical astronomy did not transcend rudimentary calendar-making (day count and solar and lunar phenomena) until the end of the second century B.C. the cosmos changed when the political order changed fundamentally. According to the Ch’in chronology, the centralized imperial state was formally inaugurated in 221b.c, but it was finally consolidated near the end of the second century B.C.

I don't know about the Chinese, but I've always been fascinated with solstices and equinoxes and their importance in ancient cultures and religions with regard to time of the year, harvest, etc.

I'm not sure what you're asking. It seems to me that you've answered your own question. You can read about the history of the Chinese calendar at this link:

http://www.math.nus.edu.sg/aslaksen/gem-projects/hm/Chinese_Calendar.pdf