what was the first time patient 28959 had the maximum platelet count value until 06/2103?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 28959 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'platelet count' ) and strftime('%y-%m',labevents.charttime) <= '2103-06' order by labevents.valuenum desc, labevents.charttime asc limit 1