Think about the theme. The phrase means seize the day. Make the most out of life. This is the focus of your poem. Keep the tone inspirational, but not preachy. There is a fine line between inspiring readers and preaching to them. Find the line and stay on the inspirational side.
Consider that a carpe diem poem can be written in any style, using any of the many rhyme and meter schemes available to a poet. A carpe diem poem is about content, not rhyme and meter.
Start with a line about time passing. For example, \"Time shows no mercy.\" Try it as a first line and build something around it that illustrates how we might let time pass us by.
Time shows no mercy
GO
Time never sleeps.
We contemplate our future
While time never creeps
Along.
We waste the seconds, the minutes,
The days of our lives
While time passes by.
Write a second stanza that turns the poem around and leaves a positive message that inspires readers not to be one of the people in the first stanza that lets time go by. For example:
Stand up and claim it,
The life that is yours.
Time to step out from
Behind closed doors.
In this stanza the use of the word time is more positive than in the first. This is like round two of a fight. In the first, time is winning. In the second, time is a tool for change.