In my opinion, the significance of this title is mainly a figurative one -- the title emphasizes one of the major themes that the author is trying to convey.
I think that a major theme of this story is that we human beings really do not have a good way to know other people. We think we can tell who is honest and who is not, but we are really not able to do this. If this is the case, we can compare our perceptions of other people to dusk. Dusk is a time when you can still kind of see the world around you, but it is not very clear. You might think you see things, but you might be wrong.
So the author is using this title, in my opinion, to show that we cannot understand other people any more clearly than we can see in the dusk.