Special meetings may be called by the Clerk on the written request of the Mayor or any three (3) members of the Council on at least eighteen (18) hours written notice to each member of the Council served personally or left at the member's usual place of residence by the City Clerk or the Clerk's designee. However any special meeting at which all members of the Council are present or have waived notice in writing, shall be a legal meeting for all purposes, without such notice.