In the mayor-aldermen plan, the mayor shall devote full time to mayoral duties and shall receive such salary as may be designated by the charter, or by ordinance if the charter so authorizes. In the council-manager plan, the mayor shall not be full-time as to the daily administrative responsibility, and authority for city operations shall be vested in the city manager. The aldermen or councilors shall be compensated in an amount not to exceed in aggregate a sum fixed by the charter, or by ordinance if the charter so authorizes.