The best solution is to wire the unit correctly: there are TWO power connections to the empeg: one for permanent (battery) power, and the other for connection to the ignition switch power.

But back to your original question: The Hijack menu has a "Screen Blanker" function, which by default will ALSO put the player into standby mode 30-minutes after the screen blanker activates. In the car, this should actually power-off the player.

EDIT: The 30-minutes timeout can be customized in the config.ini file:

[hijack]
;@DC standby_minutes=5

Cheers