Length of wait spelled out in detail, maybe to extremes (4,4)
I believe the answer is:
lead time
'length of wait' is the definition.
(time it takes to complete something)
'spelled out in detail maybe to extremes' is the wordplay.
'spelled out in' is an anagram indicator (a different spelling).
'to extremes' means to remove the middle letters.
'maybe' with its middle taken out is 'me'.
'detail' with letters rearranged gives 'leadti'.
'leadti'+'me'='LEAD TIME'
(Other definitions for lead time that I've seen before include "What will American magazine editor do" , "Interval between the start and completion of a production process" , "Gap between initiation and completion of a production process" , "I'm elated over advance period before start" , "Period between start and finish of production process" .)