when was the last time during this month that patient 92788 had the minimum lactate value?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 92788 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'lactate' ) and datetime(labevents.charttime,'start of month') = datetime(current_time,'start of month','-0 month') order by labevents.valuenum asc, labevents.charttime desc limit 1