37 CFR § 42.102 - Time for filing.
(a) A petition for inter partes review of a patent must be filed after the later of the following dates, where applicable:
(1) If the patent is a patent described in section 3(n)(1) of the Leahy-Smith America Invents Act, the date that is nine months after the date of the grant of the patent;
(2) If the patent is a patent that is not described in section 3(n)(1) of the Leahy-Smith American Invents Act, the date of the grant of the patent; or
(3) If a post-grant review is instituted as set forth in subpart C of this part, the date of the termination of such post-grant review.
(b) The Director may impose a limit on the number of inter partes reviews that may be instituted during each of the first four one-year periods in which the amendment made to chapter 31 of title 35, United States Code, is in effect by providing notice in the Office's Official Gazette or Federal Register.Petitions filed after an established limit has been reached will be deemed untimely.