The poem is a tiny scene: someone arrives home late at night and finds an owl sitting on the only step. That's all that happens, but the way it's told makes it feel larger. The title, "Auspex," is a Latin word for a person who read omens from birds, so the owl seems less like an animal that happens to be there and more like a sign, something to be read.
The last two lines turn the scene personal. Night "comes to me" as if it were a person, and the speaker admits to being "late to her bed." That image makes night feel like a patient companion or a lover who has been waiting, and the speaker sounds a little sheepish, as though they've kept her waiting too long. The mood is hushed and intimate, with a hint of the uncanny. The short lines and the single step leave a lot of silence around the words, so the owl and the dark seem to be quietly watching.