Interest must be paid upon any overpayment of the tax due under NRS 375A.100 at the rate of interest set by the Executive Director pursuant to NRS 375A.205. Except as otherwise provided in NRS 360.320, the interest must be allowed from the date on which payment of the tax would have become delinquent, if not paid, or the date of actual payment, whichever is later, to a date preceding the date of the refund by not more than 30 days, as determined by the Department.