Wash. Rev. Code § 87.03.255
Upon the day specified in the notice required by RCW 87.03.250 for the meeting, the board of directors, which is hereby constituted a board of equalization for that purpose, shall meet and continue in session from day to day as long as may be necessary, not to exceed ten days, exclusive of Sundays, to hear and determine such objections to the said assessment roll as may come before them; and the board may change the same as may be just. The secretary of the board shall be present during its session, and note all changes made at said hearing; and on or before the 30th day of October in each year to and including the year 1923, and on or before the 15th day of January beginning with the year 1925 and each year thereafter he or she shall have the assessment roll completed as finally equalized by the board.
RCW 87.03.255