If, due to circumstances beyond the control of the applicant, the construction of required improvements to the land cannot be completed within the prescribed time, the Planning Board may grant a time extension for legitimate reason, for a period of time determined by the Planning Board, to be appropriate to ensure satisfactory completion of all improvements. During such time extension, all guarantees shall remain in full force. Such requests for an extension of time shall be made in writing to the Planning Board at least sixty (60) days prior to expiration of the original security.