Leaving the car on a jack stand overnight should not be much problematic. In case the back of the vehicle is on the ground, verify whether the wheels have been choked and the parking brake has been set properly prior to keeping your vehicle at rest during the night. In case you are living with somebody, inform him or her regarding the fact that your car has been left on jack stands and they must not touch the jack stands, the Jack, or even the vehicle while it is in the air. Moreover, do not allow the family pets and the kids to wander into the garage unnoticed. In case the vehicle is positioned outdoors in an area which is not that secure, make it a point to lower the vehicle onto the ground so that hooligans are not able to mess with the Jack, use it for stealing the wheels, and so on.