Upon its completion the commissioners shall return their assessment roll into court, and thereupon the court shall make an order setting a time for the hearing thereon before the court, which day shall be at least thirty days after the entry of the order. The commissioners shall give notice of the assessment and of the day fixed by the court for the hearing thereon in the following manner:
(1) They shall at least twenty days prior to the date fixed for the hearing on the roll, mail to each owner of the property assessed, whose name and address is known to them, a notice substantially in the following form: