No improvements, buildings, facilities or other improvements of any character may be constructed upon, or may occupy or use any portion of, the Planned Residential District without a performance bond or a performance escrow sufficient to ensure the City, either of the completion of any improvements except buildings shown on the plan or alternatively, to pay the cost for restoring the site to a condition consistent with the landscaping plan, including all public improvements and off-street parking, should the project not be completed within twenty-four (4) months of approval of the final development plan. Such bond or escrow shall be in such form and amount as directed by the Mayor and Board of Aldermen; provided, that the Board of Aldermen, for good cause shown, may extend the time limits stated herein.