53 Pa. C.S. § 8431
(a) Filing.--A petition is timely filed if the letter transmitting the petition is postmarked by the United States Postal Service on or before the final day on which the petition is required to be filed. Deadlines for filing petitions are as follows:
(1) Refund petitions shall be filed within three years after the due date for filing the report as extended or one year after actual payment of an eligible tax, whichever is later. If no report is required, the petition shall be filed within three years after the due date for payment of an eligible tax or within one year after actual payment, whichever is later.
(2) Petitions for reassessment of an eligible tax shall be filed within 90 days of the date of the assessment notice.
(b) Contents.--The governing body shall adopt regulations specifying the form and content of petitions, including the process and deadlines.
53 Pa.C.S. § 8431