(b) (1) An automatic extension of six months for the filing of its annual return shall be allowed any taxpayer, if, within the time prescribed by the preceding paragraph, such taxpayer files with the tax commission an application for extension, in such form as said tax commission may prescribe by regulation, and pays, on or before the date of such filing, the amount properly estimated as its tax, as provided in paragraph two of this subdivision.

(2) If a taxpayer, within the time prescribed by subdivision (a) of this section, shall have applied for an automatic extension of time to file its annual return and shall have paid to the commissioner of taxation and finance on or before the date such application is filed an amount properly estimated as hereinafter provided in this subdivision, the only amount payable in addition to the tax shall be interest, at the underpayment rate set by the commissioner pursuant to section one thousand ninety-six of this chapter, or if no rate is set, at the rate of six per cent per year, upon the amount by which the tax, or the portion thereof payable on or before the date the return was required to be filed (determined without regard to any extension of time for filing such return), exceeds the amount so paid. For purposes of this subdivision an amount so paid shall be deemed properly estimated if it is either not less than ninety per cent of the tax as finally determined, or 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.

(c) The tax imposed by section two hundred ninety shall be payable to the tax commission in full at the time the return is required to be filed. Such tax imposed on any taxpayer which ceases to be subject to the tax imposed by this article shall be payable to the tax commission at the time the return is required to be filed and all other taxes of any such taxpayer, which pursuant to the provisions of this section would otherwise be payable subsequent to the time such return is required to be filed, shall nevertheless be payable at such time.

(d) The tax commission may grant a reasonable extension of time for filing a return or for payment of a tax imposed by this article under such conditions as it deems just and proper.