Re: 24:00 versus 00:00

From: Markus Kuhn <Markus.Kuhn_at_CL.CAM.AC.UK>
Date: Thu, 16 Feb 2006 19:53:22 +0000

Steve Allen wrote on 2006-02-16 19:25 UTC:
> > No reply from an NTP server shall ever represent any point in time
> > between 23:59:60 and 24:00:00 of a UTC day.
> Minor point, I think it has to read more like this
> between 23:59:60 of a UTC day that ends with a positive leap
> second and 00:00:00 of the subsequent UTC day.

I disagree.

With the 24-h notation, it is a very useful and well-established
convention that 00:00 refers to midnight at the start of a date, while
24:00 refers to midnight at the end of a date. Thus, both "today 24:00"
and "tomorrow 00:00" are fully equivalent representations of the same
point in time. The 24:00 notation for midnight is very useful for
writing time intervals that end on midnight. "Today 23:00-24:00" is simply
much neater and less cumbersome than "today 23:00 - tomorrow 00:00".

Writing "24:00" to terminate a time interval at exactly midnight is
pretty common practice and is even sanctioned by ISO 8601. None of this
contradicts the rule that for unambiguous representations of independent
points in time (e.g. on a clock display), as opposed to interval
endpoints, only the 00:00 form should be used.

See for example the railway timetable on

where trains arrive at 24:00 but depart at 00:00.


Markus Kuhn, Computer Laboratory, University of Cambridge || CB3 0FD, Great Britain
Received on Thu Feb 16 2006 - 11:53:42 PST

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