what was the last time that patient 27451 had a maximum value of mchc during the first hospital visit?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 27451 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'mchc' ) order by labevents.valuenum desc, labevents.charttime desc limit 1