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What is the significance of this formulation:

"31st January, Sunday, Midnight 2016"

It means 12:00 am on January 30 (the beginning of the January 31) or 12:00 am on January 31 (the end of the January 31)?

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    We generally think of the day as starting at the stroke of midnight. So 31st and 12*am* at the beginning of the day.
    – shawnt00
    Jan 30, 2016 at 18:12
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    12:00 AM is part of the following day.
    – user3169
    Jan 30, 2016 at 18:19
  • @shawnt00 am, of course, thanks for the correction. So this date comes after about 5 hours and 30 minutes in UK time?
    – Rumata
    Jan 30, 2016 at 18:40
  • @user3169 So this date comes after about 5 hours and 30 minutes in UK time?
    – Rumata
    Jan 30, 2016 at 18:41
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    Yes. It will be midnight in London in about 5 hours.
    – shawnt00
    Jan 30, 2016 at 18:42

2 Answers 2

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I think it means 12pm (00:00/24h) in 31st January, then, literally it's 1st February. Because, indepently it's EXACTLY 1 February, it is refered to the midnight of 31st January.

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    First, midnight is by convention 12am, not 12pm. The logic goes like this: 11:59:59pm (late evening) is followed by 12 midnight, which is followed by 12:00:01am, and it makes more sense for the "am"/"pm" indicator to change at the same time as the hour, so 12:00:00 gets "am" as well. Second, midnight on a date is conventionally the start of the date, not the end.
    – Mark Reed
    Jan 10, 2022 at 22:39
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By convention, 12:00am on a date is the midnight at the start of the date, not the end of it; the "am" indicates that it goes with the subsequent minutes (e.g. 12:01 am) and not the previous ones (e.g. 11:59 pm).

Since it says midnight on Sunday, January 31st, 2016 (and January 31st, 2016 was indeed a Sunday), the usual assumption would be that it represents midnight at the start of that date. In other words, one minute after 11:59pm on Saturday night the 30th.

If the time were given using 24-hour format, then labeling midnight as 00:00 makes it even more unambiguous. However, you also then have the option of using 24:00 on the previous date, though this is not allowed in e.g. ISO 8601 timestamps.

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