Interest, as provided in the Tax Administration Act [Chapter 7 Article 1 NMSA 1978], shall be paid to the state on the amount of tax due under the Estate Tax Act [7-7-1 to 7- 7-12 NMSA 1978], from the first day following the day on which payment of the tax would be due in the absence of an extension of time, until the day paid, whether or not the personal representative is granted an extension of time within which to file the federal estate tax return.