Late winter period possibly framing occasionally duller literary setting (11)

'late winter period' is the definition.
The definition suggests a singular noun which matches the answer.

'framing occasionally duller literary setting' is the wordplay.
'framing' is an insertion indicator (inserted letters are framed by the outside letters).
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'literary setting' becomes 'midmarch' (I can't explain this - if you can you should give a lot more credence to this answer).
The alternate letters of 'duller' are 'dle'.
'dle' inserted inside 'midmarch' is 'MIDDLEMARCH'.

'possibly' is the link.

Can you help me to learn more?