After the public hearing on the proposed improvement and after the council has moved to proceed with the improvement, and after giving notice of the proposed assessment as provided in section 7.500, it may pass an ordinance assessing the various parcels of real property to be specially benefited with their apportioned share of the cost of the improvement but the passage of the 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.