Time zones around the world were created by governments in response to the needs of railway companies. That is, in the 19th century railways started creating timetables, which meant they needed a standardized time system that applied over a large area and were not set to the local noon of each city. Railways were one of the chief ways that modern time discipline was imposed on ordinary people. If you look at old train stations there is almost always a huge clock on the front of the building, which was both a practical help and a symbol of modern discipline, and riding on (or working for) the railway was one of the first things that forced people to time things down to the minute.

Needless to say, China needed to get with the program. How could China make the trains run on time like a modern nation without having a time system? In the early republic the government began shifting to the solar calendar from the lunar one (a change with is still not entirely complete today). This was quite in keeping with the old idea that the Emperor decreed the calendar, but now the new government was imposing a modern time system on the country. The first system of time zones was decreed by the China Central Observatory in 1918-19. There were five time zones, although only one, the Central (Zhong Yuan) GMT +8, based on Beijing, really mattered since all the railways were in that zone, and there were plenty of local time systems that kept going alongside this. The Nationalist government kept this system, although they measured Central time from Nanjing (same zone as the city they now called Beiping, so no real change). During the war with Japan Gansu-Sichuan time became the standard. The Communists decreed Beijing time as the single standard for the whole country in 1949, although this did not really become effective till 1952 or so. It is worth noting that almost all of the conquest of China by CCP troops happened in 1948-9, and the PLA really imposed the single zone time system at first. Xinhua radio also used Beijing time.

This single time zone was not that big a change, since most of the railways and modern institution were still in the single central zone. In Xinjiang they have a “local time” (Beijing -2) that tends to be used by non-Han people, so there is still not an entirely uniform system.

Reddit has a map of the Republican zones, if you trust Reddit

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Posted by u/WildWestAdventure

https://www.reddit.com/r/MapPorn/comments/a0doa3/time_zones_of_republic_of_china_19181949/

Sources

Köll, Elisabeth. Railroads and the Transformation of China. Cambridge, Massachusetts: Harvard University Press, 2019.

Guo, Qingsheng (2001). "A Study on the Standard Time Changes for the Past 100 Years in China" China Historical Materials of Science and Technology 22.3 https://web.archive.org/web/20161220074304/http://sourcedb.cas.cn/sourcedb_scr_cas/zwqkk/kxwhzl/kxjss/jxdkjs/200912/P020091229393382424589.pdf