If you have an immigration case, the most recent decision was probably entered by a circuit court of appeals. Supreme Court Rule 13.1 states that the deadline to file a petition for a writ of certiorari is 90 days from the date of entry of judgment by the the Court of Appeals.
"1. Unless otherwise provided by law, a petition for a writ
of certiorari to review a judgment in any case, civil or criminal,
entered by a state court of last resort or a United States
court of appeals (including the United States Court of Appeals
for the Armed Forces) is timely when it is filed with
the Clerk of this Court within 90 days after entry of the
judgment. A petition for a writ of certiorari seeking review
of a judgment of a lower state court that is subject to discretionary
review by the state court of last resort is timely
when it is filed with the Clerk within 90 days after entry of
the order denying discretionary review."