On vs At with date and time

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.

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.

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.

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.