How do you guys decide when a session ends?

In Fate, there is some maintainance and advancement happening when a new session starts. However, this being online, it's basically one extended session. How do you guys tend to distinguish between different sessions in a game on this site?

I try to say when one major event in the story takes place determines the length of a session.

Sounds like Viking1031 does it about like I do. I also like to keep an eye on how much real-world time has passed. Sometimes I'll call it "end of session" in the middle of an arc just because it's been a few months. People tend to like chances to "level up" when it is that sort of game.

Sounds good. I'll probably go with significant events, it should be pretty easy to figure out.