We run promotions that end at midnight. I.e. 24:00. So if I want something to run from the 24th to the 25th it really means 0:00 24th -> 0.00 25th as far as the implementation details go. Should I tell humans:

  1. Promotion ends on the 25th

  2. Promotion ends at midnight on the 25th

  3. Promotion ends at 23:59 on the 25th

  4. Promotion ends on the 24th [since it stops after the 24th is over]

Which is prefered? Is there a better way?

  • "If I want something to run from the 24th to the 25th it really means 0:00 24th -> 0.00 25th" - this means that the promotion will run for 24 hours not 48. Your system needs to be changed so that the end time is 23:59:59 of the date.
    – dnbrv
    Mar 23, 2012 at 13:04

1 Answer 1


Not sure this is the right forum for this, but:

Your current examples refer to different times, but the approach of #3 is common and unambiguous.

In the US, we have no term that explicitly refers to the end of the day, like "24:00". Although one might argue that this is how "midnight" is used and interpreted, or how it should be, using it this way will result in confusion. Perhaps because it has no contrast, like "00:00", some people consider it to be equivalent to "12:00 AM" (i.e., a time, rather than a word we use to designate the end of the day), which is necessarily the beginning of the day. I think it makes more sense to think of midnight as an instant, that does not sit on either day.

Saying "through [date]" could work, but as with "on [date]" some people might question whether or not the cutoff time is the end of the day.

  • Your last two paragraphs are a bit confusing, but I totally agree with the first: common and unambiguous wins out. There is no way you could interpret "23:59 on the 25th" as anything other than one specific time. As Steve Krug says: Don't Make Me Think, and that's what options 1,2 and 4 do. Time spent having to think about the meaning of something is time spent being fustrated.
    – JonW
    Mar 22, 2012 at 20:44
  • I'm Swedish so the ISO standard for date with "military time" (like Americans like to refer to it) i.e. yyyy-mm-dd 24:00 is completely natural to me. :) 24:00 and 0:00 is the exact same time, but carries slightly different meaning to me. Thanks!
    – Kit Sunde
    Mar 23, 2012 at 7:10
  • I guess I should know better than to trust the first Wikipedia page I pull up (en.wikipedia.org/wiki/24-hour_clock). If 24:00 isn't simply a way to designate the end of the day, how is it used in Sweden?
    – infoal
    Mar 23, 2012 at 8:16
  • @infoal Oh it does mean the end of the day. 24:00 is the end of the day. I was just commenting to say that 24:00 is natural to me.
    – Kit Sunde
    Mar 24, 2012 at 14:37

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