Milton opens "On Time" by telling his enemy to hurry up. "Fly envious Time, till thou run out thy race" is a dismissal dressed as a command, and the rest of the poem explains why the speaker can afford such nerve. Time, as he pictures it, is a glutton that only ever eats rubbish. What it swallows is "what is false and vain, / And meerly mortal dross", dross being the scum skimmed off molten metal once the valuable part has been refined. So "little is our loss, / So little is thy gain." Those two short lines sound like a ledger being totted up, and the sum comes out in the speaker's favour.
The portrait of Time is deliberately unpleasant. Its hours are "lazy leaden-stepping", moving at "the heavy Plummets pace". A plummet is a lead weight, so the phrase makes slowness and heaviness one idea. There is a neat paradox here: Time is ordered to fly while its hours plod, which is exactly how time feels to someone who wants a long wait to end. Then Time acquires a "womb" that "devours", a single grotesque image of birth and burial. A few lines later "entomb'd" lets us hear the tomb inside the womb. The final humiliation is that Time must eat itself: "thy greedy self consum'd". The thing that swallows everything runs out of food, and Milton treats this as plain logic.
The shape of the poem enacts its argument. Lines of ten syllables alternate with short, three-beat lines such as "And meerly mortal dross," "With an individual kiss;" and "And perfectly divine,". These work like a held breath or a moment of admiration. Rhyme is irregular too, and after the interlocked opening (race/pace, hours/devours) it mostly arrives in pairs: bliss/kiss, flood/good, divine/shine, Throne/alone. The syntax builds as well. From "For when as each thing bad thou hast entomb'd" to the end, the poem is one long sentence, and its subject, "we", is withheld until "we shall for ever sit" in the penultimate line. The reader has to climb through the clauses, just as the soul must "clime" (Milton's spelling of climb) toward the sight of God.
The ending is carefully built. The last line runs to twelve syllables, longer than any other, so it seems to stretch past the point where the earlier lines stopped. It finishes on "Time", which rhymes with "clime" three lines earlier, so the enemy's name is hauled into the soul's ascent. The word is also the last in a list of defeated things, "Death, and Chance, and thee O Time". That sudden "thee" turns from talking about Time to addressing it directly, like a captive in a victory procession, and "Triumphing" invites that reading.
Smaller echoes reinforce the reversal. At the start Time has a "race" to run. Later "Joy shall overtake us as a flood", and "overtake" is a racing word, so a different runner passes Time, and a flood is the opposite of lead-footed hours. "Individual" carries its older sense of "inseparable", so Eternity's kiss, unlike the hours, cannot be divided into counted pieces. Even clothing joins in. The soul sheds "Earthy grosnes" and is "Attir'd with Stars", as if death were a change of wardrobe.
The central idea is a Christian consolation: only what is mortal is lost to Time, while "Truth, and Peace, and Love" will shine "About the supreme Throne" for ever. Milton, best known for *Paradise Lost*, was clearly at ease with enormous subjects, and here he fits one into twenty-two lines. What makes the poem memorable is that it taunts where most poems about time mourn. Its scorn is backed by craft: the words, line lengths and one sentence reaching for its subject all make the speaker's confidence feel earned. Time is cast as a creature that outlives only its own appetite, and on that view an hourglass is a countdown to Time's own end.