Each taxpayer shall, at the time of filing its return, pay to the commissioner of finance:
(a) the amount of tax payable hereunder as the same shall appear from the face of the return, or
(b) if payments of estimated tax have been made pursuant to section 11-636 of this part, the balance, if any, of the tax payable hereunder, as the same shall appear from the face of the return, after applying thereto any payments made pursuant to said section. If the time for filing the return shall be extended, the taxpayer shall pay in addition interest at the rate of six per centum per annum from the time when the return was originally required to be filed to the time of payment upon the amount by which the tax, or the portion thereof payable when the return was required to be filed, exceeds the amount then paid:
(1) a payment made on or before the date of filing of an application for an automatic extension shall be deemed properly estimated if its either: (A) not less than ninety per centum of the tax as finally determined, or (B) not less than the tax shown on the taxpayer's return for the preceding taxable year, if such preceding year was a taxable year of twelve months; and
(2) the time when a return is required to be filed shall be determined without regard to any extension of time for filing such return.