Extremely nice, after work, I suppose (5)
I believe the answer is:
Here is my best explanation:
'suppose' is the definition.
'extremely nice after work i' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'after' says to put letters next to each other.
'work' becomes 'op' (abbreviation for opus**).
'nice' with its centre taken out is 'ne'.
'ne' after 'opi' is 'OPINE'.