31 Tex. Admin. Code § 17.40
Except as provided in § 17.44 of this title (relating to Emergency Orders), a motion for rehearing is a prerequisite to an appeal. A motion for rehearing must be filed by a party within 20 days after the date the party or the attorney of record is notified of the final decision or order as required by § 17.39 of this title (relating to Commissioner's Orders). Replies to a motion for rehearing must be filed with the agency within 30 days after the date that the party or the attorney of record is notified of the final decision or order as required by § 17.39 of this title. If agency action is not taken within the 45-day period, 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 § 17.39 of this title. 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 90 days after the date that the parties of record are notified of the commissioner's order as required by § 17.39 of this title. 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 attorney of record is notified of the final decision or order as required by § 17.39 of this title.
31 Tex. Admin. Code § 17.40