The time within which any act shall be done, as provided by these rules, shall be computed by excluding the first day and including the last, unless the last day is a Saturday, Sunday or a legal holiday, pursuant to RCW 1.16.050, and then it is excluded and the next succeeding day which is neither a Saturday, Sunday nor a legal holiday is included. When the period of time prescribed or allowed is less than seven days, intermediate Saturdays, Sundays and holidays shall be excluded in the computation.