We were on that same schedule this past December and we didn't call ahead. Actually, when we arrived (at SSR) the lobby was very quiet and our room was (of course) ready right away. On all our other trips we arrived at around noon and at that time of day the lobbys are always very busy with lines at the desk - only once were we lucky enough to have our room be ready early. So for us, arriving late worked out pretty well. We got a good night's sleep and were up and out to EPCOT early the next morning!