in what season of the year does the poem take place?

The Green Knight comes to the castle during the Christmas celebration. We learn that Arthur does not like to begin his feasts until he has heard a great tale or witnessed a great marvel. Indeed, in the midst of the feasting, a wondrous stranger bursts into the hall. The stranger is most remarkable because he is entirely green, and the poet devotes nearly 100 lines to a meticulous description of his appearance.