instruction: when was patient 10624's first minimum white blood cells ?
response: SELECT labevents.charttime FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 10624) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'white blood cells') ORDER BY labevents.valuenum, labevents.charttime LIMIT 1