I got it going on, even flip a morning song
Every afternoon, I kick half the tune
And in the darkness, I'm heartless like when the NARC's hit

from Nas – Halftime Lyrics on Rap Genius

Meaning

Nas is rapping in the morning and afternoon, fine tuning his craft and building his legacy, but when night falls; Nas turns into A Villain

NARC’s usually raid a house late at night or early in the morning so they can catch the people inside by surprise. A heartless tactic.

https://www.youtube.com/watch?v=EUbhX7xWvSI

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