When is midnight? Nomenclature question

Dave Cantor Dave at Cantor.mv.com
Mon Apr 24 13:50:00 UTC 2006

On 23 Apr 2006 at 17:48, Greg Black wrote:

> I recall when I was doing compulsory military service, they
> always solved this by saying leave ended at 2359 on the day in
> question.  Even for soldiers, this was unambiguous.

My experience in the military is different from that.  When I 
served in the US Army (from 1967 to 1970), part of the time I 
served as a company clerk.  One of the duties was to close out 
the sign-in/sign-out log book at midnight every night.
The close-out entry looked roughly like this:

    2400   Closed out.    (rank)(signature)

The date was already written somewhere above and wasn't needed in 
that entry.  We were told that times were 0001-2400, and a 
soldier could sign in (specifically from leave, by the way) at 
2400 hrs.  One MINUTE later (not one second), the time was 0001, 
the next day, and a soldier signing in then would be late 
(assuming, of course, he was due back on the earlier date).
Sometimes, there would be personnel waiting for the close-out 
entry to occur so that they could sign out on leave on the new 
day.  In that case, they would use the time stamp 0000 hrs.  

Regarding other replies in this string:

Yes, I definitely recall seeing airline schedules where
12:00 N meant noon and 12:00 M meant midnight (of the EARLIER 
day).  Sorry, I cannot produce a reference for this, so I guess 
it has to be considered anecdotal.

Using 12:00 M for noon is what I learned in junior high school, 
back in the 1950's.  We were also taught that midnight was 
properly called 12:00 p.m. (it is the last minute of the ending 
day, and is therefore 12 hours after noon, which is what 'p.m.' 
literally means).  Also, the rules for changing the clocks for 
DST were consistent with that:  going to DST meant that 1:59 a.m. 
was followed by 2:00 a.m., and then the next minute was 3:01 a.m.
In the other direction, 1:59 a.m. was followed by 2:00 a.m., 
which then was followed by 1:01 a.m.!  Sorry, I have no written 
references to back up my recollection here, so this, too, is 

And this is second-hand anecdotal:  I recall reading about a case 
in the mid-1980s where a man was given a parking ticket for 
parking sometime in the mid-afternoon in a zone marked "No 
parking 8 a.m. to 12 p.m."  The defendant said that 12 p.m. was 
12 noon, but the judge said that 12 p.m. was 12 midnight, and the 
guy had to pay the fine.  Again, anecdotal, so sorry.

I found a contradictory anecdote here:  

When I worked as a system manager, I worked around the ambiguity 
problem by never scheduling anything for exactly 12:00 either 
a.m. or p.m.   I always scheduled things for 00:01, 11:59, 12:01, 
or 23:59, but I always specified 11:59 a.m. and 12:01 p.m. to 
make it clear.

As for references for usage of the word 'midnight' (as in 
"Tuesday midnight") to mean the minute before 12:01 a.m. on the 
particular day, I have no written references, but have heard this 
in context several times in informal discourse.  I did find, 
another person's statement about the confusion on the web, here:  
1.html (scroll down to "Posted by Spire").

In the original post which prompted me start this string of 
discussion, Oscar van Vlijmen quotes:

> DST starts on Sunday, April 30, 2006 at 12:00 Midnight local standard time
> DST ends on Sunday, October 1, 2006 at 12:00 Midnight local daylight time

To me, this is ambiguous.  I cannot tell whether those references 
to midnight mean the midnight which occurs before 12:01 a.m. on 
Sunday, or the midnight which occurs after 11:59 p.m. on Sunday.

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