In South Dakota, when does written notice of a recommendation to nonrenew a tenured teacher need to be made?

Under South Dakota law, after a teacher is in or beyond the fourth consecutive term of employment as a teacher with the school district (i.e., a "tenured teacher"), SDCL 13-43-6.1 and SDCL 13-43-6.2 apply to any nonrenewal of the teacher's contract. On or before April fifteenth, the superintendent or chief executive officer shall notify the teacher and the school board in writing of the recommendation to not renew the teacher's contract.