The meaning of a wall clock time is based on the legal jurisdiction of where the clock is located. It is the local law which sets the daylight savings time rul

The meaning of a wall clock time is based on the legal jurisdiction of where the clock is located. It is the local law which sets the daylight savings time rules. These are commonly written as TZ / tzdata / IANA names, as in “Europe/London” from the person to whom I replied. https://en.m.wikipedia.org/wiki/Tz_database https://en.m.wikipedia.org/wiki/Tz_database Even this is not enough for some edge cases like “I shall take my supper every day at 6pm, Jeeves” but one can always find exceptions to anything.