The board of supervisors not later than its first regular meeting after the occurrence of any one of the following shall set a time for the final hearing of the formation petition:
(a) Receipt of a favorable report from the department.
(b) Modification of the project by the board to conform to the recommendations made by the department.
(c) Receipt of the requisite petition after an adverse report by the department.
(d) Expiration of the time allowed for the making of a report by the department when the report has not been received within the time allowed.