for the last time during this year, when did patient 31306 get admitted via emergency room admit to the hospital?
select admissions.admittime from admissions where admissions.subject_id = 31306 and admissions.admission_location = 'emergency room admit' and datetime(admissions.admittime,'start of year') = datetime(current_time,'start of year','-0 year') order by admissions.admittime desc limit 1