Writer has month to pen a work half-heartedly (7)
I believe the answer is:
nabokov
'writer' is the definition.
(I've seen this before)
'month to pen a work half-heartedly' is the wordplay.
'month' becomes 'nov' (abbreviation for November).
'to pen' is an insertion indicator.
'work half-heartedly' becomes 'bok' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'bok'='abok'
'nov' placed around 'abok' is 'NABOKOV'.
'has' acts as a link.
Can you help me to learn more?
(Other definitions for nabokov that I've seen before include "'Russian-American author, famously of Lolita (7)'" , "Russian author" , "Lolita writer" , "Vladimir --, author" , "Russian-American novelist" .)