The witching hour is a the time of day when supernatural creatures such as witches, demons and ghosts are thought to appear and be at their most powerful, and black magic at its most effective. This hour is typically past midnight

Midnight

Midnight is the transition time period from one day to the next: the moment when the date changes. In the Roman time system, midnight was halfway between sunset and sunrise, varying according to the seasons....

 or the "time in the middle of the night when magic things are said to happen."

One of the earliest, if not the first, appearances this term makes is in Washington Irving's

Washington Irving

Washington Irving was an American author, essayist, biographer and historian of the early 19th century. He was best known for his short stories "The Legend of Sleepy Hollow" and "Rip Van Winkle", both of which appear in his book The Sketch Book of Geoffrey Crayon, Gent. His historical works...

 short story The Legend of Sleepy Hollow

The Legend of Sleepy Hollow

"The Legend of Sleepy Hollow" is a short story by Washington Irving contained in his collection The Sketch Book of Geoffrey Crayon, Gent., written while he was living in Birmingham, England, and first published in 1820...

.