Is going to cut short boring drunk just after sunset (8)
I believe the answer is:
twilight
'just after sunset' is the definition.
(I've seen this before)
'is going to cut short boring drunk' is the wordplay.
'is going to' becomes 'will' (John is going to eat/John will eat).
'cut short' means to remove the last letter.
'boring' is an insertion indicator (some letters must 'bore' a hole into other letters).
'drunk' becomes 'tight' (slang term).
'will' with its final letter taken away is 'wil'.
'wil' put within 'tight' is 'TWILIGHT'.
(Other definitions for twilight that I've seen before include "The last rays" , "The time between day and night" , "Period of gradual decline or obscurity" , "Vampire book" , "Glow after sunset" .)