Three short lines, and they hold a quiet kind of loss. The speaker is missing someone, though the poem never says who or why they're gone. All we get is what the speaker misses: the late night talks and the midday walks. Nothing grand, just shared time.
What stands out is the pairing of midnight and noon. Late at night, conversation tends to get honest and wandering. Midday walks feel easy and unplanned. Together they suggest that the speaker misses the whole rhythm of being with this person, from the small hours to the middle of the day, rather than any single big event.
The phrase "the most" matters too. It hints that the speaker misses other things as well, but these ordinary habits ache the worst. The mood is gentle, wistful and a little bare. There's no anger or drama, just a plain admission that everyday closeness is what you notice once it's gone.