Why is the dawn at 1000 and the dusk at 13000?
I tried looking it up on minecraft wiki but it didn't work, it kept going on about clocks. Whenever I put in the command time set day it says Set time to 1000. And when I put time set night, it says Set time to 13000. What is the system behind this?
Each hour in Minecraft is equal to 1000 Minecraft "ticks". The clock in Minecraft for a day starts at 6 AM at 0 ticks and ends at 5:59 AM on 23999 ticks. That said, Dawn is at 7 AM while Dusk is at 7 PM.
So why does the clock start at 6 AM, and why is dawn 1 hour later and not at the start? I'm not entirely sure, but from personal experience I get up to start getting ready for work at 6, the sun is at times starting to rise at 7 AM (seasons and the equinoxes need to be factored in).
I'm not sure if it's like that with the rest of the world or Sweden (I’m quite sure Mojang is based there) but we can assume that a 12-hour cycle is used so people don't complain about having more night than day when building on the surface.
You can read up more on Minecraft's day-night cycle here.
The actual system can get a bit detailed but I can give you an explanation about the numbers above. First, an in-game hour is 1000 of those units long. It runs on a 24 hour cycle as you would expect so the time goes from 0 to 23999. A complete cycle takes about 20min of real time and the translation between in game time and real time is where it can get detailed (you get into the 20 ingame ticks per second and things like that which is the rate at which the game checks to update the things around you) so I will skip it.
What is important to note here is that 0 is not Midnight like in real life. What you observed is correct, the sun comes up close to 0 instead of being the center of the night. Likewise the sun has set at 13000 and it is then considered night time. When you ask for Day or Night you are just asking for specific counts to when the sun is considered Up vs the moon being Up.
Hope this helps.
Its safe to assume that notch based the time off the 24 hour time format and offset it for ease of use. If it lined up properly, 000 (zero hundred hours aka 1am) would line up with 0 MC ticks, 1200 with 12000 and so on. Its rather strange and if it were me I wouldn't have offset it but it's not my game!
The time is offset forward by around 6 hours. If you want 13:00 for example, you'll have to use /time set 19000. Keep in mind that you should roll over at 23999, which means to get 20:00, you'll have to use /time set 2000.
