Well-wisher to finish after half a day (6)
I believe the answer is:
friend
'well-wisher' is the definition.
(thesaurus)
'finish after half a day' is the wordplay.
'finish' becomes 'fri' (I can't justify this - if you can you should believe this answer much more).
'after' becomes 'then'.
'half' indicates taking half.
'a day' becomes 'd'.
'then' cut in half is 'en'.
'fri'+'en'+'d'='FRIEND'
'to' is the link.
Can you help me to learn more?
(Other definitions for friend that I've seen before include "one quaking in society?" , "allowed to pass by the guard" , "Organisation's supporter" , "Buddy, chum" , "Buddy, mate" .)