In eases where the variance granted involves
alteration or construction and in cases approving the location of
gas stations, etc., such variance or such approval, as the ease case
be, shall expire if a building application is not filed within six
months of the effective date stated in the publication of the notice
of the filing of the decision granting such variance or approval of
such location and, if such building application is timely filed, if
such construction is not completed or substantially completed within
18 months of the effective date of the building permit.
In eases involving use variance, such variance
shall expire if such use is not commenced within six months of the
effective date stated in the publication of the notice of the filing
of the decision of the granting of the variance. Such use variance
shall expire one year after such use shall have ceased.