Time zones are complicated. Most people expect dealing with time zones to involve merely adding or subtracting a few hours from the universal time reference, UTC (Coordinated Universal Time), from −12 hours to +12 hours.

However, reality shows otherwise: time zones are not logical or predictable. There are time zones with 15-minute granularity; countries that change time zones twice a year; countries that use a custom time zone during summer, known as daylight saving time, that starts on different dates; plus tons of special and corner cases. These make the history of time zones interesting but also complicate ...

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