When the final day for payment of any tax or any installment thereof occurs on Saturday, Sunday or a legal holiday, payment may be made without interest or penalty on the following business day.
Conn. Gen. Stat. § 12-169
(1949 Rev., S. 1850; February, 1965, P.A. 26; P.A. 13-276, S. 39.)
See Sec. 12-39a re payment date for state taxes when last date is Saturday, Sunday or holiday.