(a) Oral hearing. Any party present or represented at an oral hearing, desiring to file any written argument or brief, proposed findings of fact, conclusions, and order, or statement of objections to rulings made by the presiding officer, must so inform the presiding officer at the oral hearing; upon being so informed, the presiding officer shall set a reasonable time for the filing of such documents, and state it on the record at the oral hearing.

(b) Written hearing. After filing of the last evidence in a written hearing, notice shall be served on each party that such party may file, within 20 days after such service on such party, written argument of brief, proposed findings or fact, conclusions, and order.

(c) Service; delay in preparation of report. If any such document is filed by any party, it shall be served on all other parties. The report shall not be prepared before expiration of such time for filing.