Section 11-635. Payment of tax

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.