If the board of adjustment is to consist of three members, when it is first appointed after June 10, 1959, the first terms shall be as follows: One shall be appointed for one year; one, for two years; and one, for three years. If it consists of five members, when it is first appointed after June 10, 1959, the first terms shall be as follows: One shall be appointed for one year; one, for two years; one, for three years; one, for four years; and one, for six years. Thereafter the terms shall be for six years and until their successors are appointed and qualified.