The speaker is caught in that uneasy hour around six o'clock, when the day is ending and the light is going. The "owls of six o'clock doubt" are a striking image: doubt arrives like night birds, and the speaker asks them to "carry me home." It's a strange request, since the doubts are the very thing weighing on them, yet they are also asked to bring the speaker to safety.
The second stanza turns warmer and simpler. "Whither come my rabbits" suggests the speaker is calling to something gentle and small, perhaps the creatures of evening, or perhaps the quiet thoughts that follow the doubt. Then the language settles into a short chant: "good fire good charcoal good night." With no punctuation, the words feel like a slow exhale.
The mood moves from restlessness to comfort. Doubt doesn't vanish, but it gives way to warmth, rest, and the plain pleasure of ending the day by a fire.