when was the last time that patient 31482 had a minimum calcium, total on their current hospital encounter?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 31482 and admissions.dischtime is null ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'calcium, total' ) order by labevents.valuenum asc, labevents.charttime desc limit 1