In computing a period of days for the purposes of this subchapter, unless otherwise provided by statute, the period begins on the day after the act, event, or default in question and concludes at the end of the last day of that designated period, unless that day is a Saturday, Sunday, or legal holiday on which the office of the executive director is closed, in which event the period concludes at the end of the next day that is not a Saturday, Sunday, or legal holiday.