I was confused about this a while back. Then I had the thought what time is 12:01 AM? Why, it's in the morning. And 12:01 PM is in the afternoon. Of course 12:00 AM is midnight! And of course 12:00 is noon! The hours for 12 AM and 12 PM run a full hour. They don't have some strange identity crisis twice every day one minute into that hour. Pick any other minute in that hour and it's absolutely clear which is which.