I suggest that noon needs to be designated 12: 00 M.
Not AM or PM, upright “M”.
“AM” ability “ante meridiem”, which is Latin for “sooner than mid-day”, or noon. “PM” is “put up meridiem”, or “after mid-day”.
Midday is neither sooner than noon (AM), nor after noon (PM). It's exactly mid-day. So upright call it 12: 00 M “meridiem”.
Hour of darkness is every twelve hours sooner than the following noon, so it's AM, and it's also twelve hours after the outdated noon, so it's PM. Hour of darkness is thus 12: 00 A/PM.
That need to aloof end the confusion.