Chapter 3 Authentication for FortiOS 5.0 : Configuring authenticated access : Authentication timeout : SSL VPN authentication timeout
  
SSL VPN authentication timeout
You set the SSL VPN user authentication timeout (Idle Timeout) to control how long an authenticated connection can be idle before the user must authenticate again. The maximum timeout is 28 800 seconds. The default timeout is 300 seconds.
To set the SSL VPN authentication timeout - web-based manager
1. Go to VPN > SSL > Config.
2. Enter the Idle Timeout value (seconds).
3. Select Apply.