Time artist spent unwisely in part of church (8)
I believe the answer is:
transept
'part of church' is the definition.
('transept' is part of 'church')
'time artist spent unwisely' is the wordplay.
'time' becomes 't'.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'unwisely' indicates anagramming the letters.
'spent' with letters rearranged gives 'nsept'.
't'+'ra'+'nsept'='TRANSEPT'
'in' acts as a link.
(Other definitions for transept that I've seen before include "Part of church intersecting nave" , "Cross-aisle in church" , "Section of church" , "always running north to south" , "Arm of church body" .)