Each resolution or ordinance providing for the appropriation of money, or for the annual tax levy, or for improvements petitioned for by the owners of a majority of the adjacent property to be benefitted and specially assessed therefor, and any emergency resolution or ordinance necessary for the immediate preservation of public peace, health, welfare or safety, shall take effect, unless a later date be specified therein, upon its approval by the Mayor, or upon the expiration of the time within which it may be vetoed by the Mayor, or upon its passage after veto by the Mayor, as the case may be.