When is 'midnight on the 31st May'

[RustyBear]

I received an email at 8.30am this morning from our recycling service, inviting me to enter 'May's second prize draw' telling me I had 'less than 24 hours left to cast your entry' The linked web page stated I had until midnight on 31st May to enter, but also that the draw had already closed 'at 00.00 Sunday 31st May 2020.'

So when would you say 'midnight on the 31st May' actually is?

I would have said the next evening - 12 midnight between 31May and 1 June.

Same. 12pm at the end of 31st May.

One minute after 23:59 on 31st May.

I've had this debate before, but 00:00:00 is the first second of the new day and 23:59:59 is the last second of the old day. So if the deadline was 'midnight on 31st May', you've missed the deadline. It's 12 AM, which is morning.

"One minute after 23:59 on 31st May."
"Same. 12pm at the end of 31st May."

No, you can't have 2 12PMs in one day. The 12 PM is already in the middle of the day. So the one at night has to be 12 AM.

I didn't include this in my OP as it's not strictly relevant to my main point (when is midnight on 31st May), but in the Terms and Conditions for the draw it states that the draw closes:
'in the case of an entry made via the Greenredeem website, by 23:59 hours on the last day of the preceding calendar month to which the relevant Prize Draw takes place'

This wording is confusing because the 'last day of the preceding calendar month to which the relevant Prize Draw takes place' surely must actually mean the last day of April for a draw made in May. For a monthly draw it should read the 'last day of the calendar month in which the relevant Prize Draw takes place' [my bolding]. However it definitely states 23.59 on the last day of the month.