Quit when holiday's cancelled (5,3)
I believe the answer is:
leave off
'quit' is the definition.
(I know this)
'holiday's cancelled' is the wordplay.
'holiday' becomes 'leave' (I've seen this before).
'cancelled' becomes 'off' (similar in meaning).
'leave'+'off'='LEAVE OFF'
'when' is the link.
(Other definitions for leave off that I've seen before include "not eating or drinking" , "Cease, or shed garment" , "Give over!" .)