Quits, briefly, the night before (3)
I believe the answer is:
eve
'the night before' is the definition.
(I've seen this before)
'quits briefly' is the wordplay.
'quits' becomes 'even' (as in 'call it quits').
'briefly' means to remove the last letter.
'even' with its final letter removed is 'EVE'.
(Other definitions for eve that I've seen before include "'All About - - ' (Bette Davis film)" , "Girl" , "Period immediately before" , "Day before Christmas" , "Night before an event" .)