pitch dark vs witching hour

pitch dark

witching hour

noun
  • The hour between 3:00 a.m. and 3:59 a.m., associated with demons. 

  • The hour after midnight, when witches and other supernatural beings were thought to be active, and to which bad luck was ascribed. 

How often have the words pitch dark and witching hour occurred in a corpus of books? (source: Google Ngram Viewer )