While driving through West Bend, Iowa, Alvin is seen driving past the Grotto of the Redemption from right to left. This would be north to south, or following the jog in the highway, traveling east to west.
Early in the film it was established that it is "harvest time". As Alvin is on his journey a slew of bicyclists pass him and later he motors into their camp. The only explanation for this event would be RAGBRAI, which happens in mid-late July.