Except as otherwise provided in this article, a nonresident owner of a passenger car which has been registered for the current calendar year in the state or country of which the owner is a resident and which at all times when operated in the Commonwealth displays the license plate or plates issued for such vehicle in the place of residence of such owner, may operate or permit the operation of such passenger car within or partly within this Commonwealth for a period of six months without registering the passenger car or paying any fees to the Commonwealth. If, however, at the expiration of such six months the passenger car is still in the Commonwealth, its owner shall apply for registration of the vehicle and shall pay a fee for such registration based on the time operation of the vehicle in the Commonwealth commenced.