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This must be a simple question for a native speaker.

I know that we use "on" with dates: I'll see you on January 1st.

And we use "at" with times: I'll see you at 17:30.

But what preposition has to be used when we speak for date and time:

I'll see you on January 1st at 17:30. looks ok.

But what in this case: It happened on 2014-01-01 17:30.

Is "on" correct when we are specifying the date and the time?

The date-time comes as a ready text as 2014-01-01 17:30 and I cannot modify it. I can only put text before the date-time string or after it.

Miroslav Popov
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  • Few native speakers would ever write the date and time like your 4th example. It would almost always be written like your 3rd example (or some variation thereof) – ElendilTheTall Jul 07 '14 at 11:41
  • I need this text in log written from software product. There is an event and a time stamp. I have to put some preposition between them. – Miroslav Popov Jul 07 '14 at 11:42
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    In that case it would be exactly the same as your third example - the construction is the same - on DATE at TIME – ElendilTheTall Jul 07 '14 at 11:43
  • I cannot put "at" between the date and time. The time stamp comes as string like: 2007-04-01 22:00 – Miroslav Popov Jul 07 '14 at 11:45
  • Well, leaving aside the fact that you probably pretty easily could just concatenate 'at' into the timestamp string, on would have to do. Considering it's just a log the grammar matters less than the information therein, surely? – ElendilTheTall Jul 07 '14 at 11:46
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    Time of occurrence: 2014-01-01 17:30 – mplungjan Jul 07 '14 at 11:53
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    Any reasonably competent person would understand a single preposition, but if you want to be correct about it, two is the way to go. – ElendilTheTall Jul 07 '14 at 12:07
  • Thank you! I'll use two prepositions. Can you post your comment as an an answer, in order to accept it and close the question. It looks like that this is a specific case with a little meaning out of its context. – Miroslav Popov Jul 07 '14 at 12:10
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    If you really are limited to one preposition I would use 'at', since the date & time as stated is precise to the minute. That requires 'at'. – WS2 Jul 07 '14 at 12:24
  • @WS2 that was my thought also. Since the time stamp is precised, I thought I should use at. – Miroslav Popov Jul 07 '14 at 12:26
  • "It happened on "+timeStamp.replace(/ /," at "); – mplungjan Jul 07 '14 at 15:12
  • But I wouldn't try and make a verb out of 'precise'. It is unnecessary anyway. You could say 'Since the time stamp is specific to the minute', or '...precise to the minute'. – WS2 Jul 07 '14 at 15:54
  • I'm voting to close this question as off-topic because it is not asking for advice on standard English, but on how to make standard English rules apply in a situation they're not designed for. If there is a standard choice here, the answer belongs in say a thread in ComputerSE tagged 'vocabulary'. – Edwin Ashworth Jun 13 '19 at 10:00

4 Answers4

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The construction for your fourth example would be the same as your third:

on DATE at TIME

While most people would understand it without the AT, it is strictly correct to include it.

ElendilTheTall
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    I finally chose a single preposition form with "at". Because the time is the meaningful info. A real example from the software is: Big Gap of bar 403 at 2007-04-01 20:00. – Miroslav Popov Jul 07 '14 at 19:55
  • @ElendilTheTall, So is it at 8am 2016-06-06 or is it on 8am 2016-06-06? – Pacerier Nov 18 '16 at 02:16
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As far as I know from my teaching experiences; you should consider the smallest time unit when using a prep. As follows; It happened in 2014 It happened on 2014-01-01 It happened at 2014-01-01 17:30 I hope this helps.

S. T.
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  • This does make sense, as this defines precision of date-time value - speaking about year, month, day, or exact time. – kravemir Nov 08 '20 at 11:05
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In computing, the notion of date and time is often amalgamated into a single entity, a datetime.

It may be required that a datetime is presented in a particular format. An example datetime expressed in ISO 8601 may take the form 2019-06-12T14:07:38Z. The problem is that these standardized datetimes do not naturally blend into English text. Neither It happened on 2019-06-12T14:07:38Z nor It happened at 2019-06-12T14:07:38Z are standard English.

I would argue that 'at' is the better option since we are referring to a moment in time rather than to a day as 'on' would imply.

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    While this is useful information, I don't believe it answers the question from 2014, which was about the difference between using at and on when using plain language dates and times. – Davo Jun 12 '19 at 14:45
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    @Davo Please read the question author's comments. He is coming from a computing background and is asking precisely about the scenario in my answer. –  Jun 12 '19 at 15:05
  • Like this one: *I have to put some preposition between them* ? It's not a question about formatting date time stamps, it's a question about the use of on and/or in when listing dates and times in plain language. – Davo Jun 12 '19 at 20:12
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    @Davo 'I cannot put "at" between the date and time. The time stamp comes as string like: 2007-04-01 22:00' - miroslav-popov –  Jun 13 '19 at 07:16
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    @GrantZvolský is correct. The time stamp comes as a ready-made text. It would be overkill to parse it, having into account that the exact format is unknown, only to set a preposition. – Miroslav Popov Jun 13 '19 at 09:21
  • Now that this additional information has been incorporated into the question, I concur. However, this does essentially invalidate the answers (including the accepted answer) from 2014. – Davo Jun 13 '19 at 11:09
  • I favor "at" to explain some event occurrences. In application logs, the analysis for events requires accuracy to milliseconds (nanoseconds). Can anyone understand my description like this? I found an error log record about our server failed to receive the corresponding response after it sent a query request at 2024-12-22 12:27:38.123, while Wireshark showed TCP retransmission (time-out) around that time point. – samm Jan 06 '24 at 15:47
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You would always use both.

Let's do something at TIME on DATE

You could abbreviate the "at" out in some circumstances but only when facilitated by grammar and cadence... And even then, it's still implied:

Shall we meet on DATE... around TIME?

Oli
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