crack of dawn vs sundown

crack of dawn

noun
  • The first moment of daylight; before sunrise. 

sundown

noun
  • Sunset. 

  • A hat with a wide brim to shade the eyes from sunlight. 

verb
  • to experience an episode or an onset of some detrimental mental condition like agitation, anxiety, hallucination or dementia, daily at nightfall. 

How often have the words crack of dawn and sundown occurred in a corpus of books? (source: Google Ngram Viewer )