Special meetings may be called by the mayor or any four council members, upon twenty-four hours written notice to every member of the council; provided, that the requirement of notice shall not be binding in any special meeting at which all members of the council are present without objection. Such notices may be served by any member of the police department or any other person in the City, and it shall be the duty of the city clerk when given such notices to serve the same or cause the same to be served immediately.