Of the directors elected at the next general state election following the election at which the district is created, those three elected by the highest vote in a five-ward district, or those four elected by the highest vote in a seven-ward district, shall hold office for four years, and the other two in a five-ward district and the other three in a seven-ward district for two years, and until their successors are elected and qualified. Thereafter, at each biennial general election, a number of directors corresponding to the number whose term of office expires shall be elected for terms of four years. The terms shall commence on the first Monday after the first day of January

next following the election.