I have been going through the 2006 unofficall disney transportation guide to the parks. According to them it takes 16 - 17 minutes to get to downtown disney with a car but 47 - 62 by disney bus. Now I did this trip a couple of time in October and it took about 20 minutes by bus. Has anyone else found that the times given by the book are slightly inaccurate.
I think what they are trying to give you is worst case scenario if you have just missed a bus, so the time will include journey time plus maximum wait time for the next bus. The actual bus journey time will be far shorter. Hope this helps,