If a petition for a declaratory order is set for specified proceedings under RCW 34.05.240 (5)(b), the agency shall give not less than seven days advance written notice of the proceedings to the petitioner and all persons described in RCW 34.05.240(3). The notice shall contain the time, date, place, and nature of the proceedings and shall describe how interested persons may participate in the proceeding. Pursuant to RCW 34.05.240(7), the agency may not enter a declaratory order that would substantially prejudice the rights of a person who would be a necessary party if the person does not consent in writing to the determination of the matter by a declaratory ruling proceeding.