The poem is called "To the Virgins, to Make Much of Time." The poem is addressed, presumably, to a group of virgins, and it encourages them to make the most of their time… which turns out to mean "get married before you're too old." Really? Yep. Granted, the poem is a little more elegant than that (it contains some pretty stanzas about the rising and setting of the sun, flowers, and youth and vigor) but it's pretty clear that making the most of time involves not sitting around and avoiding marriage.
It might seem strange that the poem thinks of marriage as a way to make "much of time." However, we have to consider that Herrick wrote it in the 1600s. People didn't live as long in those days, and marriage was an even bigger deal than it is now. (People took the whole no-sex-before-marriage thing more seriously, for one thing.) If you were a woman, marriage would have been really important if you wanted to be taken care of (women couldn't really get jobs), have a nice home, even have sex. If marriage could potentially provide these things in ways that the single life could not, it would indeed make sense to think of getting married as making the most of one's time.
If you were changing this poem up to fit the 21st century, what kinds of activities would you encourage young people to do in order to make "much of time"?