(1) An owner of property within the district or a person interested in a contract or proposed contract that is the subject of a validation petition may appear and answer or otherwise plead in response to the validation petition:
(a) at any time before the hearing under Section 17B-1-1203; or
(b) within any additional period of time that the district court allows.
(2) If a person fails to appear and answer or otherwise plead in the time allowed under Subsection (1):
(a) the allegations of the validation petition shall be considered admitted by that person; and
(b) that person may not participate in the validation proceedings.