how many days have it been since the first stay of patient 18866 on their current hospital visit in the careunit micu?
select 1 * ( strftime('%j',current_time) - strftime('%j',transfers.intime) ) from transfers where transfers.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 18866 and admissions.dischtime is null ) and transfers.careunit = 'micu' order by transfers.intime asc limit 1