Chat time doesn't count, I don't think.
To recap the answer to that age-old question: the BetterMost system logs you out if you have been inactive for 15 minutes. You can watch it happen on the "Who's Online" page. When someone reaches the 15 minute mark of being on the same page, they disappear. So if you were dancing in the middle of your room, and every 14 minutes and 55 seconds you went over and clicked on a BetterMost page, but then went back to dancing, and kept doing that every 14 minutes and 55 seconds, it would look like you were on here all day long, even if you didn't read or write a thing. But I don't think most of us do that. I think that mostly, we can't use the "I keep it minimized on my desktop" claim.