When such an ordinance is adopted within the time period specified in Section 11-43A-70, the council-manager form of government under this article shall become effective for such municipality either (i) immediately upon receipt of preclearance of such ordinance by the United States Department of Justice under the Voting Rights Act of 1965, as amended, or (ii) upon the first Monday in October following the next regularly scheduled municipal election, whichever effective date is specified in the ordinance.