For being "time limited" it depends on how you log in. As a general habit (and I admit I am a bit cautious in my browsing habits) I do not permanently log into any site, nor do I typically store passwords. I believe that with no movement (leaving the screen up without shutting down) I get kicked in about 15 minutes?? I'd have to review the current guidelines, glanced at them once when the boards changed format (2 years ago now??) and then not again. I stay on site, but I am no longer logged in and cannot post or see some of the sections like the Personal page.
The time seems to be shorter on the PM page. Maybe 5 minutes Even if it is a short (for me) message, I often get kicked back out to the general page.