5th season planed as the last from the start?

So, the 5th season, plus a movie, is going to be the end. My question is, did the writers know this way back while season 4 was airing? If you look at the dates in the new episodes, they've skipped half the school year so as to get quickly to graduation. I can't see them doing this if they were intending to do a season 6 at any point.