(1) The parties shall have 20 days from the issuance of a recommended order to file specific written objections with the board. Upon good cause shown, the board may extend the time within which the objections shall be filed. When objections are filed, the party making the objections shall serve a copy of the objections on all parties of record in the case and provide the board with proof of service. A failure to so serve, and provide proof of service shall, in the absence of good cause shown, invalidate any such objections as being untimely and the board may disregard same in making a final determination in the case.