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Hey, Spoons, how’d the move go?
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Long-distance buses and regional trains around Toronto use the 24-hour clock as well… I think that’s standard for scheduled transportation, and not a Quebec thing at all.
Well, Abby, the example you give is, to me, an example of a use within a specialised field. So people involved in the theatre profession use the 24-hour clock for task-related purposes. It’s a kind of jargon. The theatre industry doesn’t use it when communicating showtimes to the public. So it’s a specialised use, not a general one.
More thoughts…
The TTC (local buses, trains, streetcars in Toronto) uses AM and PM in their posted schedules at bus stops.
Derleth, why drop the colon? (Yes, I know many people do.) To me, the colon provides the very significant indication that 18:00 (your “eighteen hundred”) is not a simple base-ten number. Simply writing “1800” implies that the previous number was “1799”, not “1759”. And the military use of the “hundred” expression amplifies this.
I drop the colon because I always zero-pad the number so it’s four digits. Then I can mentally scan the first two numbers to get hour and the last two to get minute. Under that system, the colon is simply visual clutter.
So, 8:00 AM becomes 0800, which I can read immediately as oh-eight-hundred. It’s all very automatic.
Finally, those using the 12-hour clock tend to keep the colon in place. So I can possibly tell the difference between someone who uses 12-hour and someone who uses (my version of) 24-hour simply by noting who’s using colons.
There’s 12 noon and 12 midnight. There are no such times as 12:00 am and 12:00 pm.
The problem is that most modern ways of handling time require that an am or pm be added. Then the question becomes, what convention should be used to assign them?
A case can be made either way.
Logically, if you progress from 11:59 pm to 12:00, that should be 12:00 pm.
But just as logically, if you progress from 12 to 12:01 am, that should be 12:00 am.
The same for times approaching noon.
The usual practice is indeed to assign am to 12 midnight and pm to 12 noon, but there is nothing automatic or indisputable about doing so. And there should be no surprise that people have to think about the convention or sometimes get it wrong.
Conventions are arbitrary, pretty much by definition.
Of course it’s arbitrary. Almost everything about human language is arbitrary. “12 p.m.” is arbitrarily assigned to noon in the same way that “twelve” is arbitrarily assigned to “11 + 1.”
But this –
– is patently false.
National Institute of Standards and Technology
I guess we’re all surprised at things other people don’t know. But that’s why there’s an SDMB.
Exactly. 
BTW, “twenty-four o’clock” is at least as common as “zero o’clock”, though you can use it only to describe that precise point of time. There is no “twenty-four and thirty”, only “zero and thirty”.
Perhaps the idea is that midnight is the point where the previous and the next day meet.
I worked a late-night shift at an on-campus job at my undergraduate institution. I would finish at 1 a.m., but on my timesheet I wrote all my hours on the day I started work. For this reason I signed out at 25:00 rather than 01:00, since I didn’t want my hours distributed across two days. If I worked Wednesday night and the pay period ended on Wednesday, to be technically accurate I would have had to put the first hour of Thursday on the timesheet of the next pay period, which would mean that one hour’s pay would have to wait until the next pay period to be dispensed.
I just knew that someone somewhere would actually come up with a coherent use for “25:00”…
As I recall 12 midnight was 2400, and then it switched to 0001.
I have read things like “25:00” on protocols, for example. When some rules demand that a decision must be made until a certain date, there are two common tricks to archieve this despite failure to do so (Is this called an oxymoron?):
They stop the watch in the meeting room at about one minute before midnight and all subsequent events are protocolled with 23:59. This strategy could mess up with the order of events.
They do not switch to 00:00 at midnight, but rather continue counting (24:00, 25:00, …) and keep assigning the date of the previous day to events.
On review, I think this is not much different from what amore ac studio described.
Actually, in french, both are used : one can say “il est 18 heures” (“it’s eighteen hours”, litterally) or “il est 6 heures” (“it’s six hours” still literally), possibly adding “de l’apres-midi” or “du soir” (“in the afternoon” or “in the evening”) if needed. However, it seems to me that “il est 18 heures” tends to become slightly more common.
The NIST quotes are interesting, but it’s an appeal to authority that is clearly overwhelmed by reality, including a number of other authorities, such as style guides. They do nothing to support the statement that “There are no such times as 12:00 am and 12:00 pm,” a statement that, as I said before, is patently false. Language, particularly American English, is not defined by authority.