The speaker daydreams about a time before people invented ways to count time, and keeps asking the same question: were we happier then? The refrain, "I think of a time when there was no time," comes back three times, like a thought the speaker can't shake. Between those lines, the poem builds up what we gained by measuring time: hours, days, months, years, appointments, deadlines, and clocks that need winding every night. Against all that, the past seems calm, free of "hustle and bustle."
The last stanza shifts, though. The speaker wonders about giant trees, fire-breathing dragons, cave-dwelling humans, and whether God existed. These questions mix fact, legend, and belief, which suggests the speaker doesn't really know what that distant past was like. The mood is wistful and a little weary, but also uncertain. The poem never answers its question, and ending on it leaves us wondering whether the "happier" past is real or just something we imagine when life feels rushed.