"5 O'Clock" is a song by American singer T-Pain, which serves as the second official single from his fourth studio album, Revolver. Featured on the song as guest vocalists are American rapper Wiz Khalifa and British singer Lily Allen. The song contains very heavy use of autotune. It peaked at number ten on the Billboard Hot 100, becoming Allen's first and only top ten single in the United States.

Lily Allen's part in the song is sampled from her 2009 single "Who'd Have Known", which in turn resembles Take That's 2007 single "Shine". "5 O'Clock" was released on iTunes on September 27, 2011, and has been released on U.S. Mainstream radio since October 18. The song was the last release by T-Pain under the now-defunct label Jive Records. The single was released in Allen's native United Kingdom on 4 December 2011. The official remix to the song features Lily Allen and Puerto Rican duo Wisin & Yandel. The remix was released on iTunes on November 18, 2011. Other remixes were made by artists like Nelly, Young Kye, and DJ Unk. The radio version of this song cuts T-Pain's second verse. There is also another version of this song that cuts Wiz Khalifa's rap, which was included on the compilation album Now That's What I Call Music! 41.

^*sales figures based on certification alone
^{^}shipments figures based on certification alone

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