when was patient 60219 last having the minimum value of platelet count since 81 months ago?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 60219 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'platelet count' ) and datetime(labevents.charttime) >= datetime(current_time,'-81 month') order by labevents.valuenum asc, labevents.charttime desc limit 1