Assessment districts shall complete the assessment appraisal records on or before February 1. The records shall be delivered to the county assessor as of that date and any work which is the responsibility of the local assessor which is not completed by February 1 shall be accomplished by the county assessor or persons employed by the county assessor and the cost of such work shall be charged against the assessment district as provided in section 273.064. Extensions of time to complete the assessment appraisal records may be granted to the local assessor by the county assessor if such extension is approved by the county board.