Forum marks threads I haven't read as read

The forum marks posts/threads I haven't read as read. I'm not sure of the criteria, but it might be marking them as read when they're about 12 hours old. I have no way to see what I actually have/haven't read. If you can adjust this, I'd prefer as long a time as possible before the forum marks threads as read/old. I'd plan to visit the forum on a daily basis, so something longer than 24 hours would be helpful, given my routines. I can see others visiting a lot less often than daily of course. My favorite vBulletin forum marks things read after 10 days.

Yep I am experiencing a similar problem.

The system marks threads you haven't read yet. That resets when you either log off (or your computer is turned off) or clear your browser cookies/history. The idea being when you log back in, the highlighted forums have new posts since your last log out.

No, it marks them as read on its own after about 12 hours.

I believe it's controlled by Session Timeout in Cookies and HTTP Header Options: http://www.vbulletin.com/docs/html/vboptions_group_http
It's probably set to 43,200 seconds now. It may reset every time you visit the forum, so people on here constantly wouldn't notice this... not positive about that.