Brian pretty much summed it up. We aren't tooking our horns, but Brian and I are pretty much pro's at this. He does this for a living, I've been doing car illustrations for 25 years (mostly airbrush, ink, pencil... marker).
My C6 concepts can take easily 3-4 hours. Some longer. But, I make BIG detailed pics, and I'm anal. To an amatuer, maybe 15-20 hours.
I've been using Paint Shop Pro for 5 years, so I don't even THINK when I am drawing. I have it in my head and it comes out in the picture. I am on "auto-pilot" when I use the software. I'm not evening aware of what I am clicking. It just happens.
Much like anything, you have to start somewhere, like you are.
I would start with a better and bigger picture than you are starting with. Find a nice big sharp C5 pic, and just play around. Also, take some time and study reflections. Even if you have a die-cast car on your desk, it's a good reference to see how light works, and how reflections work.
Take your time, go slow - you'll get better at using the software every day. Oh, and have fun!
:thumbsup: