31 Tex. Admin. Code § 2.23
Except as provided in § 2.27 of this subchapter (relating to Emergency Order), a timely motion for rehearing is a prerequisite to an appeal. A motion for rehearing must be filed by a party not later than the 20th day after the date the party or the attorney of record is notified of the final decision or order as required by § 2.22 of this subchapter (relating to Commissioner's Orders). Replies to a motion for rehearing must be filed with the agency not later than the 30th day after the date that the party or the attorney of record is notified of the final decision or order as required by §2.22. If agency action is not taken within the 45-day period after the date the party or the party's attorney of record is notified of the final decision or order as required by §2.22, the motion for rehearing is overruled by operation of law 45 days after the date the party or the attorney of record is notified of the final decision or order required by §2.22. The commissioner may, by written order, extend the period of time for filing motions for rehearing and replies and for agency action on a motion for rehearing except that an extension may not extend the period for agency action beyond the 90th day after the date that the party or party's attorney of record is notified of the commissioner's order as required by §2.22. In the event of an extension, the motion for rehearing is overruled by operation of law on the date fixed by the order or in the absence of a fixed date, 90 days after the date the party or the party's attorney of record is notified of the final decision or order as required by §2.22.
31 Tex. Admin. Code § 2.23