Neb. Rev. Stat. § 19-608

If the city manager plan of government is approved by a majority of the electors voting thereon, such plan shall go into effect immediately as it applies to the nomination and election of officers provided for in sections 19-612 to 19-613.01 , and in all other respects such plan shall go into effect on the first Monday following the next regular municipal election. If the proposition to adopt the city manager plan of government is rejected by the electors, it shall not again be submitted in such city within two years after the proposition is rejected.