The Email Security.cloud Quarantine portal (https://eu.quarantine.symantec.com or https://us.quarantine.symantec.com) times out before saving changes to an email template or while performing administrative tasks.

The Email Quarantine portal Idle time log out is 5 minutes.

Session timeout defines the action window time for a user. The idle timeout limits the chances of an attacker to guess and use a valid session ID from another user. 

As a security best practice it's good to set the session timeout to the lowest value possible depending on the context of the application.