Taxes on unsecured personal property, and the taxes on all assessments of possession of, claim to or right of possession of land are delinquent at five p.m., on August 31st, unless August 31st falls on Saturday, in which event the time of delinquency is 5 p.m., on the next business day, regardless of when the property is discovered and assessed, and thereafter a delinquent penalty of ten percent attaches to them; provided, however, that in no case shall such penalty be less than fifty cents; provided further, that in those cases where there is both a failure to return within the time required by law and nonpayment of such taxes prior to the time they become delinquent, only one penalty shall attach. (Prior code § 6.04.1040)