Ill. Admin. Code tit. 53 § 100.130
Within 30 days from the adjournment of the hearing and with leave of the Board, each party may submit proposed Findings of Fact and Conclusions of Law. With leave of the Board, those Findings of Fact and Conclusions of Law may be supported by written briefs and arguments. For good cause, the Board may permit the parties to propose Findings of Fact and Conclusions of Law orally and on the record prior to the adjournment of the hearing. For good cause, the Board may permit non-parties to submit written briefs and arguments. In determining whether or not to permit the submission of Findings of Fact and/or Briefs, the Board shall consider but is not limited to, the complexity of the issues involved; the familiarity of the Board with regard to the subject matter; and the diligence of the parties involved.
Ill. Admin. Code tit. 53, § 100.130