And what is this longer form presentation about? Per Animation Scoop:
... The epic adventure centers around Mordecai and Rigby who, after accidentally creating a Timenado, have to go back in time and battle an evil volleyball coach in order to save the universe…
Regular Show, one of the pillars of Cartoon Network, was renewed for a new season in July. When you rank near the top of the cartoon pack, you get a feature to go with your TV half-hours.
H/t Animation Scoop.