Within 10 days after the service of such a notice, the person upon whom notice is served may demand a hearing upon the necessity for the closing of the kelp bed or beds, or parts thereof. Upon such demand for a hearing, the commission shall fix a time and place for the taking of evidence upon the necessity for the closing, which time shall be not less than 10 days nor more than 30 days from the date of such demand. The department shall serve written notice of the time and place of the hearing upon the person demanding the hearing, at least 10 days before the day set for the hearing. If no demand is made for a hearing within the time prescribed the kelp bed or beds, or parts thereof, shall remain closed to the harvesting of kelp for the time mentioned in the order.