Not really, it can certainly take one hour or all day. I think it starts with a detailed discussion about the car with its owner, then some time for the photographer to generate a vision of how each important detail is best showcased. Then there is always set-up time, using different angles at differnet settings of the same detail, getting a good motion shot, etc..

Dont get me wrong, the location is sometimes very important, but I just dont think it it should be the primary focus for a car shoot, which after the 3rd or 4th image into a 20 image set, it becomes more about the location if only the outside of the car is shown at 20 different ones.