What time of year is it in "The Death of the Hired Man" by Robert Frost?

The conversation between Warren and Mary in "The Death of the Hired Man" takes place in the winter.

Mary begins the conversation with Warren because Silas, their "hired man", has returned.  Silas wants to stay, but Warren does not want him to.  Silas had let Warren down the last time he was there, leaving right during haying time when his help was sorely needed because he wanted "a little pay", and Warren could not "afford to pay any fixed wages".  Warren says, "Off he goes always when I need him most...In winter he comes back to us...I'm done".

Mary has found Silas "huddled against the barn-door fast asleep, a miserable sight".  She is worried, because he seems much changed from when they saw him last.  Mary says Silas is "worn out", and "kept nodding off" when she tried to talk to him.  He did say that "he'd come to ditch the meadow", and "to clear the upper pasture, too".

Warren is scornful of Silas's promises; apparently he has heard them all before.  Mary agrees, and says that this time, Silas seems disoriented, being unable to distinguish between the past and the present.  She acknowledges that "his working days are done", and says "he has come home to die".