2 final characters in single day (7)
I believe the answer is:
sozzled
'2' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I can't see?
'final characters in single day' is the wordplay.
'final characters' becomes 'ZZ' (two Z's - Z is the end of the alphabet).
'in' is an insertion indicator.
'single' becomes 'sole' (synonyms).
'day' becomes 'd' (abbreviation for day).
'zz' going within 'sole' is 'sozzle'.
'sozzle'+'d'='SOZZLED'
Can you help me to learn more?
(Other definitions for sozzled that I've seen before include "Sloshed" , "Drunk" .)