A long time back for example visiting S Africa (4)
I believe the answer is:
ages
'a long time' is the definition.
(I've seen this before)
'back for example visiting s africa' is the wordplay.
'back for' says the letters should be written in reverse (I've seen 'backing for' mean this).
'example' becomes 'eg'.
'visiting' is an insertion indicator.
's africa' becomes 'sa'.
'eg' inserted into 'sa' is 'sega'.
'sega' backwards is 'AGES'.
(Other definitions for ages that I've seen before include "Sage (anag)" , "Rock of - - (hymn)" , "Aeons" , "Grows old like sage" , "Matures" .)