A long time that is wasted in kiss (5)
I believe the answer is:
yonks
'a long time' is the definition.
(I've seen this before)
'that is wasted in kiss' is the wordplay.
'that' becomes 'yon' (archaic term meaning 'that').
'wasted in' is a deletion indicator.
'kiss' with 'is' taken away is 'ks'.
'yon'+'ks'='YONKS'
(Other definitions for yonks that I've seen before include "Ages (informal)" , "An age" , "A very long time (colloq.)" , "Many years (slang)" , "Slangily, a long time" .)