when's the first time patient 83894 had the minimum hemoglobin in their last hospital encounter?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 83894 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'hemoglobin' ) order by labevents.valuenum asc, labevents.charttime asc limit 1