I watched "The Best Day Ever" again. Arthur said that Buster was gone for a whole year! Originally, I thought that he was gone for the summer. For my fanfics I decided that he was gone for about two weeks during the month of September.

Arthur may have been exaggerating to emphasize how long it seemed like Buster was gone, because during the era of Buster being away with his father, I believe it was only two-three months or so.