Any probationary or permanent certificated employee whose contract of employment may be amended, terminated, or not renewed for the next school year shall be notified in writing on or before April 15 of each year of such possible action on the contract. If the certificated employee wishes a hearing, a written request shall be sent to the secretary of the school board or the superintendent of schools or the superintendent's designee within seven calendar days after receipt of the written notice. Unless (1) continued by written agreement between the parties or their representatives as provided in this section or (2) a hearing officer is utilized as provided in sections 79-840 to 79-842, final action by the school board must be taken on or before May 15 of each year. If a hearing on amendment, nonrenewal, cancellation, or termination is not requested within the time provided for in sections 79-824 to 79-842, the school board shall make a final determination. With regard to all hearings provided for under such sections, either formal due process hearings or informal hearings, the certificated employee shall be advised in writing at least five days prior to the date of hearing of the date, time, and place of the hearing. Except as provided in section 79-840, all such hearings shall be held within thirty days of the date of the request for hearing. The parties or their representatives by mutual agreement, confirmed in writing, may extend the times for hearings or final determinations by the board under sections 79-824 to 79-842.