I’ve never seen anyone use the abbreviations MN or NN, although they would certainly clear up some confusion for a lot of people. AM and PM are correct.
12MN is an abbreviation of 12MidNight and 12NN is 12NooN. The usage varies from country to country.
Depends on what time it is. If it’s midnight then 12am is correct. If it’s noon then 12pm is correct.
You use 12MN when you refer as the 24th hour of the day. Exactly. And 12NN as the 12th hour of the day. Exactly. In a 12 hour clock between 12:01-11:59 in the morning is AM. And the second 12 hour between 12:01-11:59 is PM. So when the clock strike at 12nn that means 12:00 sharp in the afternoon. And when it strike at 12mn it means in the middle of the night almost morning.
So I say 12MN when you refer as 12 o clock sharp in the morning and 12NN when you refer as 12 o clock sharp in the afternoon
12pm is midnight – twelve hours after noon. 12am is also midnight – twelve hours before noon. As long as we use a twelve hour clock with times before and after noon, there will always be ambiguity. If you are using a twelve hour clock, call it noon and save any problems. Better still, use a twenty-four hour clock.
What is correct is 12:00AM for midnight and 12:00PM for noon.
However….I use 12M and 12N and no one has misunderstood me yet.