It's all based on the strategus/CRPG time. I don't know how many hours in a day there are in CRPG (EDIT: Durr, I mean, how many real-time minutes are in a CRPG hour), but if you look at the website (where your character is) you will see an icon in the top left displaying what time it is. When you join a server you will experience the time and weather displayed there (which is why someone joining a game later than others can experience different weather and time of day. Unless they changed the way it works)