The cookie time-out in the session state of the virtual directories should match the license session time-out property set in the system settings within console.. Article Increasing the session idle timeout time for Web Access explains how to change the session time-outs. The rest of the settings on the session state page can be left as default
The frameworks timeout can be left at 20 mins because Console has the ability to re-authenticate you automatically if the session has timed out as it keeps your login credentials handy on the client side. In Web Desk the user session data kept in the Service Desk database is automatically cleared after 20 minutes (value set in the license session timeout property in console) of inactivity by the Background Processing service.
It should be noted that increasing these timeouts also means that if a license is locked for any reason then the time it takes for that license to be released will also be increased. This is explained in more detail on page 149 of the LANDESK Service Desk 7.8 - Administrator Guide.