Three questions about midnight.

Using the twelve hour clock, is midnight denoted

12:00 (midnight)

or

00:00?

Using the twenty four hour clock, is midnight denoted

24:00

or

00:00?

Is midnight an instant of the day just ending or the day just
beginning? I.e. if I _now_ use the phrase "midnight today", do I refer
to a time past (about 18 hours ago), or a time yet to come (in about 6
hours)?

Ray.Milne...

In the Forces you LOST 2 minutes per day, which began at 0001 and ended at
2359. There was no such thing as midnight, 00.00 or 24.00

There may be an ISO standard, but where to find it?

Jeff Gaines...

I don't know about standards but in my experience each day ends at
midnight, i.e. 24:00 or 12:00 (midnight). That's based on things like
dates flipping over, indicators on clocks flipping from p.m. to a.m.
etc.