While I sympathize with lynnie5150, I don't trust airports, airlines, or bus lines enough to actually check bags containing expensive electronics. Always carry on laptops, cameras, video cameras, ipods, etc.--onto the plane AND onto the bus.
Last Sept, we took ME. We had an early flight. The plane landed... not sure now... maybe 10:40AM? So, the timing may make a difference. Also, we stayed at POR. Anyway, we followed the signs/directions to ME, checked in without a line and were first in line for a bus. We probably waited less than five minutes before being loaded onto a bus. Then, the bus had to pull around back somewhere and pick up luggage. After that, we were on our way. Once on WDW property, we had to drop off other people at their hotels. I did not time it, but I wouldn't be surprised if it was 60-90 minutes total.
Also, keep in mind that your plane might not be on time... and there may be more traffic at 5:30-6:30PM when you'd be on the road.
Someone in FL (or a more frequent traveler) might know better than I would, but I think you can figure at least 30 minutes of driving time, no matter how you do the drive (own car, bus, etc.). Then, you have to add the extra 'steps' that I mentioned... I'd say if everything works out just right (no lines, right on a bus, traffic not bad, you're the first resort that gets dropped off), you're looking at 45 minutes minimum. I'd still say you're likely looking at 60-90 minutes from leaving the plane to standing in line at your check-in desk.