The most common and most likely answer to this crossword clue is the 3 plus 4 letter word PIP EMMA
I've seen this crossword clue in The Guardian
P
I
P
E
M
M
A
More clues leading to the result PIP EMMA
Buddy explains!
The straight part
We know that "Very good Austen novel when keeping quiet in the afternoon/in the afternoon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case very good austen novel when keeping quiet in the afternoon/in the afternoon = pip emma.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.