The afternoon parade starts in Frontierland. It will reach the castle approximately 15 minutes after it starts, Main Street approx. 20 minutes after the start, and the train station approx. 25 minutes after the start. These times are based on other parades I have seen at WDW, because I always see the afternoon parade at Frontierland. Also, keep in mind that viewing will be limited if you plan on getting there right when the parade arrives. It is a popular parade.