In computing any period of time prescribed or allowed by this chapter, by order of the council, or by any applicable statute, the period shall begin on the day after the act, event, or filing in question and it shall conclude on the last day of the designated period, unless it is a Saturday, Sunday, or state-observed holiday, in which event the period shall conclude on the next day which is neither a Saturday, Sunday, nor a state-observed holiday.
31 Tex. Admin. Code § 655.65