N.Y. Comp. Codes R. & Regs. tit. 9 § 2529.2
A PAR against an order of a rent administrator must be filed in person, by mail, or otherwise as provided by operational bulletin, with the DHCR within 35 days after the date such order is issued. A PAR served by mail must be postmarked not more than 35 days after the date of such order, to be deemed timely filed. If the prepaid postage on the envelope in which the PAR is mailed is by private postage meter, and the envelope does not have an official U.S. Postal Service postmark, then the PAR will not be considered timely filed unless received within the aforementioned 35 days or the petitioner submits other adequate proof of mailing within said 35 days, such as an official Postal Service receipt or certificate of mailing.
N.Y. Comp. Codes R. & Regs. Tit. 9 § 2529.2