the power-off option powers off everything but the CID, but not immediately.FWIW: according to the service tech I was talking to, the standard reset just resets the CID; it won't have any impact on autopilot systems. Not sure how accurate that is(perhaps @verygreen or someone can comment)
about 1.5 minutes to power AP computer down (just before it turns off you'll hear a loud fan noise from around glove box that then stops, of if it was already hot it'll just stop -that's how you know AP computer turned itself off).
Of course power off like that does not wipe any data on the AP computer so whatever calibrations it has are still retained (it does help with resetting the hung state that it enters after having 3 crashes in a row, though - manifested as no AP available and no speed limit detected anywhere).