An association may pay earnings on its savings accounts from sources available for payment of earnings at such rate and at such times and for such time or notice periods as shall be determined by resolution of its board of directors subject to such rules and regulations promulgated by the commissioner. Except for accounts which shall be classified according to a specified contractual time or notice period, earnings shall be declared on the withdrawal value of each savings account at the beginning of the accounting period, plus additions thereto made during the period (less amounts previously withdrawn and noticed for withdrawal, which for earnings purposes shall be deducted from the latest previous additions thereto) computed at the declared rate for the time the funds have been invested, which time shall be fixed by the bylaws of the association. No earnings shall be declared or paid for an accounting period unless the allocation to the general reserve for the pre ceding accounting period required herein has been made. The board of directors, by resolution, may determine that earnings shall not be paid on any savings account which has a withdrawal value of a specified amount less than Fifty Dollars ($50.00) or which by written agreement is intended to be closed within a specified period less than fifteen (15) months after the date on which such savings account is opened, provided that an exception may be made and earnings paid on savings accounts opened pursuant to Sections 81-12-129 and 81-12-131. The directors shall determine by resolution the method of calculating the amount of any earnings on savings accounts as herein provided, and the time or times when earnings are to be declared, paid or credited.