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Military time designating an unspecified time after midnight but before sunrise. Normally used in reference to either the time one goes to sleep, wakes up, or has to be on-the-job. Usually quite a while before sunrise, i.e.: well before 0500 hours ( 5AM for you civilians )

The name is a play on the way 24-hour time is handled in the Military. Times are pronounced as numbers and written without colons, i.e.: 4:30PM is 1630H or "sixteen-thirty hours". Times between midnight and noon such as 4:00AM are written as 0400 and have the leading zero called out as "zero" or the letter "O", as in "o-four-hundred".
Example: We had to get up at o-dark-thirty to get the job done this morning.
by Princess Die November 30, 2005
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Jul 6 Word of the Day
Phrase meaning that a deceased cannot rest in peace until society changes due to the circumstances of a death.
People said rest in power for the unarmed man had been shot by the police.
by FooBarBiz October 12, 2017
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2
Early in the morning before the sun is up.
Used to define when you must get up and go somewhere in the early hours of the morning between 1:30am and 5:30am.

a time in the am around the half hour mark.
"You're leaving tomarow? Will I get a chance to see you?"
"Nahh, we're taking off at o dark thirty. You won't be up yet."
by Cloudyjuicebox April 28, 2006
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3
O'Dark Thirty: (V.) Army Milspeak.
A measurement of time in the United States Army. O'Dark Thirty is usual reserved for the period between midnite and sunrise, which always is the coldest,wettest,darkest and shittiest of the year. It is also, without exception, the time of day when no sane Human Being would be found awake and/or sturring.
Q: "What time is First Formation?". A. "O'Dark Thirty; Same as always".
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4
Same as o'dark hundred. Way too fucking early to be outside working--or patrolling, if you are in the military.
By the time I got off, it was o'dark thirty.
by Rob Eichmann December 10, 2005
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5
Very early. Early enough to seriously fuck up the day before, and the day of the event in question.
Yo...we had to get up at O dark -thirty to get to the meeting on time.
by Rick Burns December 20, 2006
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6
Reeeeeallly early in the morning
"Oh my God, I was up at o'dark-thirty this morning and I can't stop yawning!"
by Alexa-in-wonderland February 04, 2010
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