Before railways, time was local. Every town set its clocks by the position of the sun, which meant that Bristol was ten minutes behind London, and Leeds was six minutes behind Birmingham. This was fine when the fastest way to travel between cities took several hours. It became a problem when trains started running timetables across hundreds of miles.
British railways solved this pragmatically in the 1840s by standardising on London time across their networks. Passengers in Bristol boarding a train scheduled to depart at 10am London time needed to account for the fact that their local clocks said 9:50. The confusion this created — two sets of clocks running simultaneously in some stations, one showing local time and one showing railway time — was the first recorded instance of timezone friction in the modern sense.
The United States formalised timezone standardisation in 1883, driven by the same railway problem at continental scale. The world followed with the International Meridian Conference of 1884, which established Greenwich as the prime meridian and divided the globe into hourly offset zones. It was a practical solution to a practical problem, and it has been accreting exceptions ever since.
China is one contiguous timezone (UTC+8) despite spanning a geographic range that would naturally cover five. This was a political decision made after 1949 to reinforce national unity. The western edge of China, where the sun does not rise until 10am by the clock, has adapted accordingly.
India sits at UTC+5:30 — a half-hour offset — a compromise between the natural solar time of its eastern and western coasts. Nepal, unwilling to simply adopt Indian time, sits at UTC+5:45. These fractional offsets are entirely rational from a geographic standpoint and entirely inconvenient from a computational one.
DST was introduced during the First World War as an energy conservation measure, abandoned, reintroduced during the Second World War, abandoned again, and then gradually reinstated across different countries at different times with different rules. The United States changed its DST dates in 2007. The European Union voted to abolish DST in 2019 but has not yet implemented the change.
The timezone map is not a clean engineering artefact. It is a geological record of political decisions, colonial boundaries, railway lobbying, wartime policy, and nationalist sentiment, accumulated over a hundred and fifty years. The abbreviations, offsets, and DST rules that developers and coordinators work with today are the sediment of that history.
It is not going to get simpler.