When, under the provisions of this title, an act is to be done within a certain time period, the time shall be computed by excluding the first day and including the last, except that when the last day is a Saturday, Sunday, or a day designated by RCW 1.16.050 or by the city's ordinances as a holiday, then it also is excluded and the act must be completed on the next business day.
RCW 35A.21.080