Except as otherwise specifically provided by commission rules, in computing any period of time prescribed or allowed by commission regulation or orders or by any applicable statute, the period shall begin on the day after the act, event, or default in question and shall conclude on the last day of that designated period, unless it is a Saturday, Sunday, or legal holiday on which the office of the chief clerk is closed, in which event the period runs until the end of the next day that is neither a Saturday, Sunday, nor a legal holiday on which the office of the chief clerk is closed.
30 Tex. Admin. Code § 1.7