Agreement to finish early -- something to enjoy (5)
I believe the answer is:
treat
'something to enjoy' is the definition.
(as in a special treat)
'agreement to finish early' is the wordplay.
'agreement' becomes 'treaty' (treaty is a kind of agreement).
'to finish early' means to remove the last letter (the letter comes to an end before its last letter).
'treaty' with its last letter taken off is 'TREAT'.
(Other definitions for treat that I've seen before include "Handle; dainty" , "Discuss" , "Apply remedies" , "Tend" , "Try to heal" .)