night shift vs nighttime

night shift

noun
  • A regularly scheduled period of work, during evening or night hours. 

  • A group of workers who work during the night. 

nighttime

noun
  • The hours of darkness between sunset and sunrise; the night. 

adj
  • Pertaining to nighttime; appropriate to the night. 

  • Happening during the night. 

How often have the words night shift and nighttime occurred in a corpus of books? (source: Google Ngram Viewer )