The board shall hear and pass upon the petition and protests at the time appointed, or at any time to which the hearing may be adjourned, and its decision thereon shall be final and conclusive. If protests are made to the formation of the proposed district or to the proposed improvement by any of the qualified voters of the proposed district as of the date of the petition or by the owners of any property which will be subject to taxation for district purposes if the proposed district is formed, then, notwithstanding the denial of any of such protests by the board of supervisors or the fact that the petition is signed by all of the owners of the real property within the proposed district, the board of supervisors shall, if it acquires jurisdiction pursuant to Section 55160, call an election pursuant to Section 55180.