Almost finishing breakfast in the dark! (5)
I believe the answer is:
night
'the dark' is the definition.
(it's dark at nighttime)
'almost finishing breakfast' is the wordplay.
'almost' becomes 'nigh' (synonyms).
'finishing' suggests the final letters (the letter which finishes the word).
The final letter of 'breakfast' is 't'.
'nigh'+'t'='NIGHT'
'in' acts as a link.
(Other definitions for night that I've seen before include "Opposite of day" , "For most, the time for sleep" , "A Hard Day's (the Beatles)" , "'The 2 8 of the dog in the _____'" , "See 8" .)