oh dark thirty

• 0-dark-thirty
• oh-dark-thirty
• zero dark thirty

From U.S. military terminology, in which hours before 10:00 am are prefixed with a zero, read as "oh", as in 0530, oh five-thirty, for 5:30 am.

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oh dark thirty

1. Some unspecified hour in the early morning (implies an unpleasant time to be awake).

   I had to get up at oh dark thirty to catch a plane.

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

• 0-dark-hundred
• oh dark hundred
• dark thirty