New answers tagged calendar
If you were on an 18th Century British warship, the day started at noon rather than midnight (12 hours behind). If you arrived in port in the afternoon and then stayed ashore overnight, your day would have been 12 hours long. Of course, if you're allowed to travel and cross the international date line, then the day can be as long or short as you like.
The day that western China switched from local time to the now-standard UTC+8 (the same as eastern China, four normal time zones away), some cities/provinces there should have experienced a 20 hour day. That may be the answer to this question. I am making this answer CW so that someone more knowledgeable can fill in the historical details.
I posit that, wherever the change occurred between the Julian calendar (O.S.) and the Gregorian calendar (N.S.), that constituted the shortest day -- indeed, a group of them -- since the span of days skipped therefore became non-existent. Those days could thus be interpreted as zero hours long.
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