What does "by Friday midnight" mean?

Going by the rules of my local post office, it means after friday just before it becomes saturday. as in, by friday including friday right up to the very last minute.

note: i live in a town that has a shop called “the 24 hour shop” that closes at 2am, my town is not exactly known for making sense on this kind of thing.

I would think that it’s Friday at 23:59. But if it were my own personal deadline, I’d definitely check with the person creating said deadline.

I would also assume 11:59PM Friday night was the last possible minute.

Friday night for me is the night that follows Friday morning and Friday evening and midnight would be the midnight that leads into Saturday but it is always best to check what the person setting the deadline means.

I’ve never heard of ‘x-day midnight’ as referring to the midnight before x-day starts. If someone asks for something by x-day midnight, and then tells you that the thing you handed in on x-day was late, well, I think that most people would support an argument that this someone is incorrect.

It’s ambiguous, to be sure. I personally would take it as 1 second past 23:59:59 Friday night. But I would ask the person to clarify.

Some definitions:

Midnight == 00:00:00 == 12:00:00AM

Date changes occur at midnight. 11:59:59PM is on Thursday. One second later is 12:00:00AM on Friday.

Merriam-Webster defines by – in this context – as “not later than”.

—

Altogether, the words themselves taken at face value would seem to mean no later than 12:00:00AM Friday morning.

but…

In my experience, and in agreement with other flutherites here, the usage of this particular vernacular implies that you have until the end of the calendar day Friday, 11:59:59PM to complete the task.

If you’re dealing with legal definition and contracts, be sure to get it in writing, and ensure they use an actual time reference, not some label like “midnight” or “oh-dark-thirty”, etc.

Agree with @poisonedantidote.

Like taxes have to be posted by midnight on April 15th means any time before the date changes to April 16th.

It depends on the person stating it. One of my professors stated the similar and she did not mean Friday night. She meant 12am on Friday morning just after Thursday. Another professor of mine meant the other referring to just before midnight Saturday or 11:59PM Friday. It is always best to check with the person to make sure you are understanding them correctly though because depending upon their background and personal views they may have a different preconception than you.