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.
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".