27 CFR 70.264: Time return deemed filed and tax considered paid.

For purposes of section 6511 of the Internal Revenue Code, a return filed before the last day prescribed by law or regulations for the filing thereof shall be considered as filed on such last day. For purposes of section 6511(b) (2) and (c), payment of any portion of the tax made before the last day prescribed for payment shall be considered made on such last day. An extension of time for filing a return or for paying any tax shall not be given any effect in determining under this section the last day prescribed for filing a return or paying any tax.