Tax Law, §§ 171, 289-d(3), 434-a(3), 514-a(2), 691(c), 1091(c), 1147(a)(3), 1419(c)
Except as otherwise provided by law or this Title, when the last day prescribed (including any extensions of time, where applicable) for filing a document, making a payment, or performing any act falls on a Saturday, Sunday or a day which is a legal holiday in the State of New York, these acts will be considered timely if performed on the next succeeding day which is not a Saturday, Sunday or legal holiday.
N.Y. Comp. Codes R. & Regs. Tit. 20 § 2399.3