ZD and LU: While “standard time” is a “modern day” invention, there were always two type of hours. The first, 12 “hours” of daylight and 12 hours of “night” commonly known as “shaah zmanios” which is used for halachic times such as Krias Shemah and Sof Zman Tefilla. In addition the chachomim understood that there were 24 hours, each hour consisting of 1080 Chalakim. This is how they calculated that each month is exactly 29 days, 12 hours, and 793 Chalakim.
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