You can use the Keep Alive operation to extend the session timeout period.
The minimum session time is currently 20 minutes (Italian Exchange). On the international (.com) Exchange the current session time is 24 hours. Therefore, you should request Keep Alive within this time to prevent session expiry.
If you don't call Keep Alive within the specified timeout period, the session will expire. Please note: Session times aren't determined or extended based on API activity.