David,

the timeout is set to 30 minutes. However if you open a new browser window I have seen it where it won't preserve the new posts from within that 30 minutes. If you get an email and click the link it pops a new window. that new window likely won't show the new posts. Only the original window you checked for new posts since the last session will preserve that or so I've seen on my system.

The browser seems to see its own session as the current one and judges everything by that rather than the server session. this is a code issue by design. I don't know if I agree with it because of the behaviour you describe but it may be something we address this year in coming versions.