So as long as I'm on the clock punching this time card
Hip-hop ain't dying on my watch

from Eminem – Rhyme or Reason Lyrics on Rap Genius

Meaning

Employees have to punch in a time card at work to mark when they arrive and leave. Since rap is Eminem’s job, “as long as I’m on the clock punching this time card” just means as long as he continues to rap. And as long as he’s rapping, he doesn’t plan on letting hip-hop die on him. Note the clock/watch wordplay.

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