RCW 70.77.460: Reports, payments deemed made when filed or paid or date mailed.

When reports on fireworks transactions or the payments of license fees or penalties are required to be made on or by specified dates, they shall be deemed to have been made at the time they are filed with or paid to the chief of the Washington state patrol, through the director of fire protection, or, if sent by mail, on the date shown by the United States postmark on the envelope containing the report or payment.