I took a look again: there's a scene transition in the form of a calendar on the wall, with all the days being marked off. The month on the calendar is May, and May 31st, according to the calendar, is a Thursday... then, we hear Buster's voice-over of his latest lunch journal, dated as June 2nd, which according to the two blank spaces on the calendar, would mean June 2nd would be a Saturday.

But yeah, where I live, the school system usually sent us kids back to school early-to-mid August or so, while the last day of school was usually like May 25 or so (ballparking it), so it always seems really strange to me whenever a kid is talking about, or still attending school, at any point during the month of June.