Unless work has materially commenced (as defined in § 270-194C) in accordance with the special authorization within one year from the issuance of the building permit authorizing such work, or within 36 months of the date the reviewing Board approved the special authorization, whichever is earlier, not only the building permit but the special authorization shall expire and the permissible uses and construction on the property shall revert to those in effect prior to the approval of any special authorization. The reviewing Board, upon request of the applicant, after a public hearing, and upon a finding that the imposition of the time limits set forth above would create an undue hardship on the applicant, may extend the time limits for such additional periods as the reviewing Board may reasonably determine. An application for such extension may be made at the time of filing of the original application or at any time thereafter up to, but no later than, six months after the expiration of the time limits set forth above.