Fun fact: Ancient Egyptians used a base 12 for time (and in some other places) because we have have 12 segments on our index through pinky fingers. They used their thumbs as a placeholder or to count. That base 12 system then turned into the 24 hour clock system we use today.
There's also evidence of an early base-12 system in use for some Indo-Europeans -- it's likely why the English morphology doesn't become compositional until 13:
12/24 is also easily divisible by more numbers: 1, 2, 3, 4, & 6
10/20 only have the factors 1 & 5
60 is divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30
100 is divisible by 1, 2, 4, 5, 10, 15, 20, 25, 50
I have no idea what's up with using am/pm when we could just use 24 hours. It makes no sense to me that someone would even think to create that. Like, "Hmmm. Okay. What if instead of 1500, we say that's 3 but in the afternoon? That way there are two 3s, and people could get more confused. Jk! It's so that the middle of the day and middle of the night are both at 12. I mean, I guess everyone would already know that 0000 and 1200 are the middle of their respective halves of the day, but let's just make both 12. There's no way this could cause any difficulties. Even if 12:45 am is before 1:15 am of the same day."
Probably something with sundials. ~6am going up to 12 at noon, then going 1-6pm if night and day are equal (I've never actually seen a sundial and I'm sure people got clever with them as time went on)
I mean a sundial doesn't even track hours so much as daylight before and after noon
In most of European countries we don’t have an equivalent of AM/PM and we mostly use 24 hours time. If not we have to add “6 of the afternoon”.
Fun fact: can you tell a difference between “midnight in the morning” and “midnight in the evening”? It seems that everyone assumes that midnight is always the end of a day, but 24h clocks never display 24:00. It’s 00:00 to 23:59