By default, JROX eCommerce Suite auto logs off the admin user if he / she is idle for a specific period of time. This is normally done after 2 hours of normal inactivity.
To increase the timer, you can edit the option in the file:
Set the following option to a higher value:
define('DEFAULT_ADMIN_SESSION_TIMER', 7200000); //2 hours 7200000
You can also disable the admin login timer in Settings > Admin > Admin Profile > Enable Admin Session Timer