The walk to the park from the parking garage is about 5-10min. Of course you also have the time it takes to drive there, possibly wait in line to pay for parking and then following the crowd to the designated parking spot. Then you have a 5-10 min walk to actually get to the park. It really does depend on what time you get there and the crowds. Staying on-site means you walk out the hotel and straight to the park or take the water taxi. Also if you stay on-site and want a break during the day just walk back to the hotel.

The benefits of staying on-site are tremendous at a busy time of year. Check-in at 8am, even if your room is not ready you can use the fastpass all day and you can use it all the last day of your stay even after you have checked out.

If you're going at a slow time and want to get hotel points then stay wherever. If you want to have a great first experience then stay on-site. It really does make a difference.