The poem is a small, strange puzzle, and it works best if you let the images stay a little unexplained. A man carries a bag home, and somehow night is inside it. Darkness arrives at noon, folded up and portable, as if he has picked up an evening the way you'd pick up groceries.
The speaker seems to feel a mix of weariness and wonder. "Late night" suggests exhaustion, or a sense that things have gone on too long. Then the horses appear, and they can't carry "us" any farther than "a light ink." That odd phrase might mean the darkness is thin and faint, like a watery stain, yet it still stops everything. The journey runs out of room.
The mood is dreamlike and quiet, a little melancholy. Nothing is spelled out, so the poem feels like a half-remembered dream, where ordinary objects hold something enormous and the logic is felt rather than explained.