what was the first time patient 9964 has had the minimum heart rate since 09/26/2104?
select chartevents.charttime from chartevents where chartevents.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 9964 ) ) and chartevents.itemid in ( select d_items.itemid from d_items where d_items.label = 'heart rate' and d_items.linksto = 'chartevents' ) and strftime('%y-%m-%d',chartevents.charttime) >= '2104-09-26' order by chartevents.valuenum asc, chartevents.charttime asc limit 1