We usually had morning ADRs to make. Our first day we left an hour early because we had no idea where we were going
It's maybe a 15 - 20 minute drive anywhere from the resort, and then budget a small amount of time to get from your car. We probably could have left 45 minutes before parking opening and been there with time to spare. Maybe even less than 45 min
You could always try it both ways and see which one works out better. We liked going to our car after parks though instead of waiting for a bus as well.