Terms. The members of the Board of Adjustment shall continue until their respective terms expire. Thereafter, the term of each member shall be four years from January 1 of the year of their appointment. The terms of members first appointed under this chapter shall be so determined that, to the greatest practicable extent, the expiration of such terms shall be distributed, in the case of regular members, evenly over the first four years after their appointment and, in the case of alternate members, evenly over the first two years after their appointment; provided that the initial term of no regular member shall exceed four years and that the initial term of no alternate member shall exceed two years. Thereafter, the term of each regular member shall be four years and the term of each alternate member shall be two years.