Sunday will end at 23:59:59 (11:59:59 pm). At 00:00:00 (12:00:00 am) (midnight), a new day (Monday) starts.

I think you are technically correct. But I don't think CO even knows. I just completed my reservation that was supposed to be held until Midnight Monday. The agent thought that would mean until the end of Monday, but I think it's actually (as you say) the beginning of Monday at 12:00am.

Here's a good way to remember it it. Just watch the ball drop in Times Square.

The second before it hit bottom it was 11:59:59, December 31. One second later it was 12:00:00 (Midnight). January 1.

But that doesn't help the ambiguity with the airline's deadline.

A little sideway thinking: it can only be 11:59 pm on that day. If it was 00:01, considering it has said "midnight" for years, there would have been countless people losing their reservations when they thought they still had a day, and CO would have been inondated with calls and complaints.

The fact that this hasn't been corrected or clarified in years means it's the later of the two possibility.

This is why the use of the 12-hour clock is fraught with peril. If the message had been created using a 24-hour clock ("We will hold your reservation ontil 24:00 Monday, 1 March...") there is no doubt that 24:00 was one minute after 23:59 on 1.3.

But here really isn't 24:00... 23:59:59 jumps to 00:00:00

Where exactly is "here"?


If you mean a clock display, yes, but 00:00:00 is the same as 24:00:00

Yeah, but is "1.3" March 1 or January 3?

Anyway, a better solution would be to set a minimum 32 hour deadline: noon CT the day after tomorrow. No ambiguity there. ^ CO can play up the extra 12 hours as a competitive perk, like they do gruel at meal times.

Actually, I've seen the use of 24:00, as well as 25:00 and 26:00 and 27:00 to indicate late night 1am, 2am, and 3am the next day. I've seen this on TV schedules as well as train/subway schedules in some countries. Although these times don't actually exist, what is meant is well understood and causes less confusion in general. For example, if train depart at 25:00 Monday, it's intuitive that it's late Monday night. If it's specified as 01:00 Tuesday, some people will not realize that this really means late Monday night.

I think it especially makes sense in the case where what is being referred to does not operate all night long. For example, if a subway system operates from 5am - 1am daily, then having the departures that depart between 12am and 1am are more intuitive if they are listed as 24:00-25:00 the previous day, especially if there are ticketing standards such as a "single-day unlimited pass" which treats the final 12am-1am hour as part of the previous day.

The use of 24:00 is quite common - some businesses are open from 0-24 for example.

So, have we agreed on whether CO has an official policy on how they use "midnight." Is it the beginning or the end of the day for them?

My post above is accurate. Whether we've agreed on that or not is hard to say based on the random other conversations here, but the answer is what it is.

Thanks Seth. So "in CO parlance midnight is 2359 Central Time on the date noted" except when it noted as "in New York/Newark, NJ (EWR - Liberty)" or when it looks at Midnight GMT as Channa speculates so it is really 5:00pm CT?

Well, midnight is 2359. If you're dealing with held tickets it is 2359 Zulu. Flight Ops are 2359 in the local time zone. And most other things that have a clock associated with them (promos, etc.) are 2359 Central.

It depends on the order of operations/precedence.
(Monday 23:59) + 1 minute = 0:00 Tuesday.
Monday (23:59 + 1 minute) = 0:00 Monday (i.e. 24 hours earlier).

IMO the first is the correct interpretation...

Exactly (except it's also true here ).

Writing 24:00 is just begging for mixups. One might as well use Monday at 72:00 to mean the midnight that occurs between Wednesday and Thursday.

People generally seem to agree that 12:00AM and 12:00PM mean midnight and noon, respectively. However, the US gov't sometimes disagrees (I've seen at least one US gov't style guide that states that 12:00AM is noon). Of course neither 12:00AM nor 12:00PM can be noon: noon is neither before (ante) nor after (post) noon.

Why companies still use "midnight" and 12AM/12PM is beyond me; it's just begging for trouble. Just add or subtract and minute or second and there is no problem to debate.