In computing any period of time prescribed or allowed in this chapter, the day of the act or event from which the designated period of time begins to run shall not be included. The last day of the period so computed shall be included, unless it is a Saturday, a Sunday or a legal holiday, in which event the period runs until the end of the next day which is neither a Saturday, a Sunday nor a legal holiday. Legal holidays are prescribed in RCW 1.16.050. When the period of time prescribed or allowed is less than 7 days, intermediate Saturdays, Sundays and legal holidays shall be excluded in the computation.