The session lifetime determines the maximum idle time of a user's Okta session. When the session expires, the Okta Session Lifetime is calculated based on the last user's action inside Okta, not on the login timestamp.

When the Okta Session ends, the user is logged out of Okta. The maximum idle time is the amount of inactive time that passes before the Okta session automatically expires, regardless of the maximum Okta session lifetime.

This article aims to explain what session-related SysLog events are triggered depending on the type of user session timeout that was triggered in Okta. 

• Global Session Policy
• System Log

Okta does not generate log events for non-explicit user logouts. That means if a user's session expires due to either idle time or max session lifetime, an event is not generated in the System Log. Okta only generates one if the user explicitly logs out by clicking the Sign out button or if an admin revokes the user's session. 

All the user session-related events (and more) are in the Event Types documentation.

If interested in Okta adding this feature to the roadmap, upvote and track the following Okta Idea.