Definition of "witching hour"

'Tis the witching hour of night, / Orbed is the moon and bright, / And the stars they glisten, glisten, / Seeming with bright eyes to listen— / ⁠For what listen they?

1818, John Keats, A Prophecy

[...] the Penzance train is shown as non-stop to Plymouth in the down direction, but in the up as being prepared to pick up sleeping car passengers at Newton Abbot, Exeter and Taunton (the two last-mentioned at the witching hours of 2.42 and 3.25 a.m.) and also to set down at Reading.

1960 March, “Sleeping Cars to the West”, in Trains Illustrated, page 173

Genie let out of the bottle / It is now the witching hour / Murderers, you're murderers / We are not the same as you

2003, “The Gloaming”, in Hail to the Thief, performed by Radiohead