The permit holder shall be obligated to commence work within 24 hours from the date of issuance, and the excavation shall be made and all necessary work shall be performed and completed within three days after commencement. However, the Director of Public Service may, in his discretion, grant a time extension which shall be endorsed on the back of the permit with the reason therefor. No time extension shall be valid unless dated and signed by the Director.
('65 Code, § 901.05)