0-dark-thirty

0-dark-thirty (uncountable)

1. (chiefly US military slang) Half an hour past 12(am) midnight, or more formal and exact would be 00:30; The practice of adding “dark” and “thirty” (30) can be used sometimes as a slang term in place of an otherwise specific time a time of night, meaning some time when it is dark out between 00:01 - 05:00 hours local time.
   • 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.

• stupid o'clock, wee small hours; see also Thesaurus:early morning

• 0-dark-hundred
• dark thirty
• oh dark hundred
• oh dark thirty
• zero dark thirty
• dark o’clock

• beer o'clock