The speaker wonders what time really is once we stop counting it in seconds, hours and days. Those units are described as "our own constructs," something people invented, so the poem tries measuring time another way: in laughter, smiles and adventures. The tone here is quietly questioning. The speaker notes that such moments feel "so far and few in between," and asks how many of them truly count, or are remembered at all.
The examples are deliberately ordinary: smiling for a camera, laughing at a joke, a week in the mountains, a night out with friends. Even the good moments seem small and easy to lose. The poem's last stanza flips the opening lines around, reordering the same phrases, which gives a slightly dizzy, circling feeling, as if time itself has become hard to hold onto. The mood is reflective and a little wistful. It doesn't offer an answer, only nudges us to wonder what we're actually keeping from our days.