Any municipality adopting a council-manager plan of government shall provide in its charter that the council members shall be elected by the voters of the municipality either:
a. At a regular municipal election held on the second Tuesday in May in the years in which municipal officers are to be elected, in which case the term of office of the council members shall begin on July 1 next following their election; or
b. At the general election held on the first Tuesday after the first Monday in November or at such other time as may be provided by law for holding general elections, in which case the term of office of the council members shall begin on January 1 next following their election.