If your camera is hardwired to your vehicles main battery then parking mode will rely on additional power available from your vehicle's battery to power the camera in parking mode. The amount of time that your vehicles battery will be able to power your camera will vary in every vehicle as there are a number of variables that affect this including: battery age, battery capacity, battery type, driving habits, vehicle type, petrol/diesel, alternator, etc.

Once your vehicle's battery voltage reaches the low voltage cut-off setting on the camera, your battery no longer has enough power to safely run the camera, and as such the camera will power down and will be unable to record until the vehicle is started again and this is to prevent the camera from fully draining and damaging your vehicles battery.

If your vehicles battery does not provide much/any parking mode, then generally in order to extend parking mode, you could to look into an external battery pack such as a BlackVue B-130X or a B-112 battery pack. This would be installed into the vehicle, and would charge any time you are driving and then power the camera separately from your vehicles battery for as long as possible. For full details on each battery pack, please see the links below:
B-130X: https://www.blackvue.com.au/accessories/blackvue-b-130x/ 
B-112: https://www.blackvue.com.au/accessories/blackvue-b-112-battery-pack/