According to the 2013 X3's manual, the parked car ventilation is simply a manual on instead of using the timer. The idea is to manually turn it on for 30 minutes after you park and leave the car. It seems like the one can doing the same thing by using the timer, set the start time to the current time. Maybe thats why BMW grey that function out.
The parked-car ventilation ventilates the vehicle
interior and lowers its temperature, if necessary.
The system can be switched on and off at any
external temperature, either directly or by using
two preset switch-on times. It remains switched
on for 30 minutes.
Open the vents to allow air to flow out.
Operation can be performed via iDrive.
Switching on/off directly
3. "Activate parked-car vent."
The symbol on the automatic climate control
flashes if the system is switched on."