Well I put in the hours on going through the model to apply shaders and textures to it, organize all the parts by identifying each one and putting them in the appropriate group, then spend hours creating and testing the look of each of the paints and surfaces in multiple environments. Once I did all that (which was an ongoing process), then I could do a render in anywhere from 3-12 minutes, depending on what was in the scene and how close the camera was to the car.
Digital gives you fantastic flexibility for changes, but sometimes the setup can be just as laborious.
Love what you're doing and seeing the work "in progress" as it were.