'To show the beldam daughters of her daughter,
To make the child a man, the man a child,
To slay the tiger that doth live by slaughter,
To tame the unicorn and lion wild,
To mock the subtle in themselves beguiled,
To cheer the ploughman with increaseful crops,
And waste huge stones with little water drops.
"To show the beldam daughters of her daughter," Time lets a grandmother see her granddaughters. Beldam is an old woman, here in its original sense of "grandmother" (it later came to mean hag), and "the daughters of her daughter" are her granddaughters.
"To make the child a man, the man a child," Time carries a person through the whole span of life and back again. The man who becomes a child is the old man in his second childhood. The line is an antithesis, with the two halves mirroring each other.
"To slay the tiger that doth live by slaughter," Even the fiercest predator falls to Time. The tiger is a stock example of a creature of pure violence, and it is the type of thing that kills others and is killed in turn. The line does not point to Tarquin. It belongs to a list of examples.
"To tame the unicorn and lion wild," The unicorn and the lion were the standard emblems of ferocity that cannot be tamed. Time does what no hunter can. Reading "unicorn" as purity and "lion" as chaos, as some commentary does, adds a meaning the passage does not need.
"To mock the subtle in themselves beguiled," Time makes fools of the cunning, who are trapped by their own cleverness. Beguiled means deceived. This is an aphorism about Time's ironies in general.
"To cheer the ploughman with increaseful crops," Time also brings good things: the harvest, increaseful meaning abundant. The list mixes gifts with ruin, and that mix is the point of the stanza.
"And waste huge stones with little water drops." A proverb (Ovid's gutta cavat lapidem, "the drop hollows the stone"). Waste means wear away. Patient, small forces defeat what looks immovable.
Lucrece is cataloguing Time's power over everything: age, beasts, cleverness, harvests, stone. The next stanza shows why she bothers. Having established that Time can do all this, she asks: "Why work'st thou mischief in thy pilgrimage, / Unless thou couldst return to make amends?" If Time can wear down stone and undo the wise, it should be able to give back one hour, and in that hour she says she "could prevent this storm and shun thy wrack." So the list builds toward a complaint. Time is powerful enough to do anything and still cannot undo what has been done to her.
The tragedy frames the speech, but the stanza itself is about Time.