Responses to discovery requests shall be made within a reasonable time period of not less than 14 days after receipt of service as directed by the party seeking discovery. The hearings officer may shorten or lengthen such time periods as the interest of justice requires. Nothing within this section shall prevent the party seeking discovery to extend response deadlines by agreement, but no such agreement shall be enforceable unless in writing and filed in the contested case that forms the basis for the discovery requests as provided in §1.31 of this title (relating to Agreements To Be in Writing).