middle day vs noontime

middle day

noun
  • Midday; noon. 

noontime

noun
  • Approximately noon. 

  • Noon. 

  • The time at which something peaks in some way (e.g., in vitality, in influence, in reknown) (by analogy with the waxing of the sun each day). 

How often have the words middle day and noontime occurred in a corpus of books? (source: Google Ngram Viewer )