session expiry and /notice/new

perhaps unlike most users, I tend to let an open identica browser window sit open and then dent at some point in the future. Unfortunately, it seems that before that inspiration hits, my session has expired. I hit the send button and nothing happens - no feedback whatsoever and the notice is not submitted. Using firebug I can see that the js/ajax/jquery client side is getting a 400 response from the server: "There was a problem with your session token. Try again, please." Since I haven't visited a page in a while, my token/session expired.
1. how long should a session last? I haven't timed it but it seems shorter than it should be.
2. should/could the js tickle laconica to confirm a session before trying to post?
3. are session lengths being thwarted by php cleanup? Check session.cookie_lifetime and session.gc_maxlifetime in php.ini.