The other biggest fun trick of timezone math to a riddle like that would be the International Date line where a baby born on one side of it can be born on the "day before" by calendar reckoning despite being born 30 minutes after the other side of the line.

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hdjrudni 14 minutes ago | parent | next [-]

Isn't that precisely the same?

Doesn't even have to be the International Date line, any two timezones work.

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rmunn 2 hours ago | parent | prev [-]

Fraternal (not identical) twins, born aboard a ship traveling west to east across the Pacific. One of them officially born January 1st, 2016. The younger-by-30-minutes twin officially born December 31st, 2015. They'll have the hardest time persuading people that they're really twins once they're grown up.

	▲	hdjrudni 13 minutes ago \| parent [-]
		This works even without timezones. If they're born even a second apart, it can so happen on different days (if they're born around midnight)