From what I can tell, user session cookies only contain data about when the session was created. In my mind, that means a user session will expire after whatever time is set in Session Config > Session timeout (Crowd) or the default session setting in web.xml (JIRA). The session is not refreshed by user activity. So, if a user logs into JIRA via a Crowd account at 10am, and the Session timeout in Crowd is set to 60 minutes, the user will be logged out at 11am, regardless of whether they've been actively using JIRA all that time.
Is that a correct understanding?