The terms of the members first appointed shall be determined by the Mayor so that to the greatest practical extent, the expiration of the 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 a regular member shall be four years; and the term of an alternate member shall be two years. All terms shall run from January 1 of the year in which the appointment was made. Notwithstanding any other provisions herein, the term of any member common to the Landmarks Preservation Commission and the Planning Board shall be for the term of membership on the Planning Board; and the term of any member common to the Landmarks Preservation Commission and the Board of Adjustment shall be for the term of membership on the Board of Adjustment.