All objections to the form, contents, validity or sufficiency of the report on the project and all objections to the form, contents, validity or sufficiency of the notice of hearing on the report shall be made in writing and filed with the clerk of the legislative body at or before the time fixed for the hearing on the report, and if not so made at such time shall be waived and no objection thereto may be made thereafter except in case of actual fraud. Any such objections shall be heard and considered and at such hearing the report may be amended in accordance with the facts, and the hearing had upon such report as so amended.