Wash. Rev. Code § 81.53.140
The commission, in any order requiring work to be done, shall have power to fix the time within which the same shall be performed and completed: PROVIDED, That if any party having a duty to perform within a fixed time under any order of the commission shall make it appear to the commission that the order cannot reasonably be complied with within the time fixed by reason either of facts arising after the entry of the order or of facts existing prior to the entry thereof that were not presented, and with reasonable diligence could not have been sooner presented to the commission, such party shall be entitled to a reasonable extension of time within which to perform the work. An order of the commission refusing to grant an extension of time may be reviewed as provided for the review of other orders of the commission.
RCW 81.53.140