The mayor and councilmen of each municipality shall be elected for terms of two or four years. Unless otherwise provided by ordinance, four-year terms shall be set so that not more than one-half of the council and mayor shall be elected in the same general election; provided, that in the first election after incorporation of a new municipality or adoption of a form of government pursuant to § 5-5-10, one-half of the councilmen may be elected for terms of two years and one-half of the councilmen and mayor may be elected for terms of four years if necessary to establish staggered terms. Two-year terms shall not be staggered.