catnap vs sack time

catnap

noun
  • A brief, light sleep, usually during the daytime. 

verb
  • To take a catnap (short sleep or nap). 

  • To kidnap a cat. 

sack time

noun
  • Time spent sleeping. 

How often have the words catnap and sack time occurred in a corpus of books? (source: Google Ngram Viewer )