"A month of winter" is a stinted use of the preposition. My answer "a month in the winter " ought to be accepted
Styczeń to miejsce zimy lub lato
The English translation for this sentence should really have the word 'the' before 'winter'.
Isn't that dependent on some dialectal differences? Anyway, that works as well.
I did a bit of research and I think you're right, it's dialect. I retract my initial comment hehe