The calculation of any time period measured in days by Finance Code Chapter 156, or this chapter, is made using calendar days, unless clearly stated otherwise. In computing a period of calendar days, the first day is excluded and the last day is included. If the last day of any period is a Saturday, Sunday, or legal holiday, the period is extended to include the next day that is not a Saturday, Sunday, or legal holiday, unless clearly stated otherwise.
7 Tex. Admin. Code § 56.5