Eastern artist’s a long time (3)
I believe the answer is:
era
'a long time' is the definition.
(I've seen this before)
'eastern artist's' is the wordplay.
'eastern' becomes 'e'.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'e'+'ra'='ERA'
(Other definitions for era that I've seen before include "Long historic period" , "Important date" , "Cycle" , "Period, age" , "Aeon" .)