Awfully odd time, in theory, to cheat (2,3,5,2)
I believe the answer is:
do the dirty on
'cheat' is the definition.
(I've seen this before)
'awfully odd time in theory' is the wordplay.
'awfully' indicates an anagram.
'time' becomes 't' (abbreviation).
'odd'+'t'+'in'+'theory'='oddtintheory'
'oddtintheory' with letters rearranged gives 'DO THE DIRTY ON'.
'to' acts as a link.
(Other definitions for do the dirty on that I've seen before include "Cheat!" , "double-cross?" .)