For all of the public retirement plans administered by the board, the board shall make monthly annuity payments on the twenty-fifth day of each month, except the month of December, when the board shall make the payments on the eighteenth day of December. If the date of payment falls on a holiday, Saturday or Sunday, then the payment shall be made on the preceding workday. All annuities shall be paid in twelve monthly payments.
W. Va. Code § 5-10D-9