We have stayed at Grande Vista which is relatively close to Vistana Villages and I would allow about 20 minutes to Magic Kingdom parking lot. Some of the other parks are a bit less. If you are needing to make b'fast ressies or something like that at MK, leave a lot more time. You'll need to park, take the parking tram, and then monorail or boat to the park...depending upon how busy it is this can take quite a while.
We drove one night to EPCOT and were able to park in one of the first few non-handicapped rows in spots people had left for the day, so that was a quick trip, but usually we allow at least 20 minutes from that area of I-Drive.