All in good time – assuming this writer's in shopping arcade (8)
I believe the answer is:
galleria
'shopping arcade' is the definition.
(I've seen this before)
'all in good time assuming this writer's' is the wordplay.
'in' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'time' becomes 'era' (an era is a period of time).
'assuming' is an insertion indicator (inserted letters are taken in or assumed).
'this writer' becomes 'I' (the person who is writing these clues).
'g'+'era'='gera'
'gera' enclosing 'i' is 'geria'.
'all' put into 'geria' is 'GALLERIA'.
'in' acts as a link.
(Other definitions for galleria that I've seen before include "Arcade of small shops" , "Shopping arcade" .)