when did patient 18678 enter the hospital via the phys referral/normal deli for the first time since 3 years ago?
select admissions.admittime from admissions where admissions.subject_id = 18678 and admissions.admission_location = 'phys referral/normal deli' and datetime(admissions.admittime) >= datetime(current_time,'-3 year') order by admissions.admittime asc limit 1