Timeless times: being inside, being outside (8)
I believe the answer is:
external
'outside' is the definition.
('external' is associated in meaning with 'outside')
'timeless times being inside' is the wordplay.
'timeless' becomes 'eternal' ('eternal' can be a synonym of 'timeless').
'times' becomes 'x' (multiplication sign).
'being inside' is an insertion indicator.
'eternal' enclosing 'x' is 'EXTERNAL'.
'being' is the link.
(Other definitions for external that I've seen before include "Relating to the outside" , "involving foreign nations" , "Outer" , "Superficial" , "Surface" .)