Green’s Dictionary of Slang

(US) unpunctuality.

1978		T. Hillerman Listening Woman 21: [Navajo speaker] Three kinds of time [...] On time, and Navajo time, and Short Mountain Navajo time.
1993		T. Hillerman Sacred Clowns 64: ‘Eight minutes late,’ she said. [...] ‘Eight minutes you don’t mention,’ Chee said. ‘You have to be a lot later than that to claim you’re working on Navajo time.’.