how many hours has it been since the first time patient 14154 got a lactate dehydrogenase (ld) lab test in this hospital visit.
select 24 * ( strftime('%j',current_time) - strftime('%j',labevents.charttime) ) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'lactate dehydrogenase (ld)' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 14154 and admissions.dischtime is null ) order by labevents.charttime asc limit 1