Very late at night, some time between midnight and dawn. Either you have to stay up very late, or you have to get up too damned early. Pronounced "oh dark thirty" or "zero dark thirty". (Derived from military time.)
My flight out's at 8 AM, so I'll have to get up at 0-dark-30 to get through security.
You are in shock, or saw the most embarrassing, horrific or satisfying thing you never found in memory, so are you ready to go hospital after that satisfying time you fainted in shock and required that slang bitch defilibrator?!