When any special assessment roll shall have been made the same shall be filed in the office of the director of public works. Before confirming the assessment roll the board of public works shall fix a time and place when it will meet and review the same and hear any objections thereto, and shall cause notice of the hearing and of the filing of the assessment roll, to be published twice prior to the hearing in a newspaper circulating in the special assessment district, the first publication to be at least 10 days before the hearing. The hearing may be adjourned from time to time without further notice. Any person objecting to the assessment roll shall file his objection thereto in writing with the director of public works before the close of the hearing or within such further time as the board may grant. After the hearing the board of public works may confirm the special assessment roll as reported to it or corrected by it, or may refer it back for revision, or may annul it and direct a new roll to be made. When a special assessment roll shall have been confirmed the secretary of the board shall indorse thereon the date of confirmation. After the confirmation the special assessment roll and all assessments thereon shall be final and conclusive unless attacked in a court of competent jurisdiction within 30 days after the date of confirmation.