Interest shall be paid upon any overpayment of any amount of tax at the modified adjusted rate per month established pursuant to Section 6591.5 from the first day of the calendar month following the period during which the overpayment was made. In addition, a refund or credit shall be made of any interest imposed upon the person making the overpayment with respect to the amount being refunded or credited.

The interest shall be paid as follows:

the case of a refund, to the last day of the calendar month following the date upon which the person making the overpayment, if he or she has not already filed a claim, is notified by the board that a claim may be filed or the date upon which the claim is approved by the board, whichever date is earlier.