(2) After the public hearing on the proposed improvement and after the district board has moved to proceed with the improvement, it may pass an ordinance assessing the various lots, parcels of land or parts thereof, to be specially benefited with their apportioned share of the cost of the improvement; but the passage of an assessment ordinance may be delayed until the contract for the work is let, or until the improvement is completed and the total cost thereof is determined. [1969 c.686 §§6,7]