The Email Security.cloud Quarantine portal (eu.quarantine.symantec.com or 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.