Your system automatically switches to standby (off) after 24 hours of non-use—which includes no remote control activity. But if the 30-minute standby timer is enabled, the system will automatically switch to standby after 30 minutes of non-use—including no audio played, as well as no remote control activity.
To enable the system standby timeout, follow these steps:
on the remote, press and hold alarm setup/menu until "-setup menu-" is displayed
press tune/playlist > eight times until "-auto off-" is displayed
press time - or time + to select "no" or "yes"
press alarm setup/menu to exit the setup menu or wait 10 seconds for the setup menu to exit automatically