instruction: when was the last time that patient 006-66039 had a maximum sao2 on 07/10/2103.
response: SELECT vitalperiodic.observationtime FROM vitalperiodic WHERE vitalperiodic.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '006-66039')) AND NOT vitalperiodic.sao2 IS NULL AND STRFTIME('%y-%m-%d', vitalperiodic.observationtime) = '2103-07-10' ORDER BY vitalperiodic.sao2 DESC, vitalperiodic.observationtime DESC LIMIT 1