In Athens, but not now (4)
I believe the answer is:
then
'not now' is the definition.
(I've seen this before)
'in athens but' is the wordplay.
'in' indicates the answer is hidden within the clue.
'THEN' can be found hidden inside 'athens but'.
(Other definitions for then that I've seen before include "Subsequently - previously" , "soon?" , "At that time; next" , "Consequently" , "Afterwards - as a result" .)