The inclusion of any property in the Potential-Landmark List: Exteriors or the Potential-Landmark List: Public Interiors, as the case may be, automatically expires: on the 180^th day after the Commission’s decision to add the structure to that List, unless, before that date, a proposed ordinance is introduced into the City Council to add the structure to the Landmark List: Exteriors or the Landmark List: Public Interiors, respectively; or if a proposed Landmark ordinance is introduced into the City Council before that 180^th day but has not yet been enacted, 18 months from the date of the proposed ordinance’s introduction. Ord. 15-408