The City agrees to modify the level of franchise fees imposed only once in any twenty-four (24) month period. Any such ordinance exempting certain types or classes of customers, or increasing, decreasing, modifying or eliminating the franchise fee shall become effective, and billings reflecting the change shall commence, on an agreed upon date which is not less than sixty (60) days following written notice to the Company by certified mail. The Company shall not be required to implement such new ordinance unless and until it determines that it has received appropriate official documentation of final action by the City Council.