0-dark-thirty

0-dark-thirty (uncountable)

1. (chiefly US military slang) Half an hour after 0-dark-hundred; an otherwise unspecified time of night; some time when it is dark out.
   • 2002, Jonathan Shay, Odysseus in America: Combat Trauma and the Trials of Homecoming

     In the very early morning--0-dark-30--the veterans have the Wall entirely to themselves, which is the main reason that we go at that hour.

• 0-dark-hundred

• beer o'clock