what was the last time until 50 months ago patient 28966 had the minimum hemoglobin value?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 28966 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'hemoglobin' ) and datetime(labevents.charttime) <= datetime(current_time,'-50 month') order by labevents.valuenum asc, labevents.charttime desc limit 1