Okla. Stat. tit. 19, § 1241

It shall be the duty of the county assessor, within five (5) days after being directed to appraise the property, to proceed to appraise and apportion the benefits to such lots and tracts of land as shall have been designated by the board of county commissioners, according to the title as aforesaid, after having taken and subscribed an oath to make a true and impartial appraisement and apportionment. A written report of such appraisement and apportionment shall be returned and filed with the county clerk within ten (10) days from the date of notice to the county assessor.