early vs oh dark hundred

early

noun
  • A shift (scheduled work period) that takes place early in the day. 

adv
  • At a time before expected; sooner than usual. 

  • Soon; in good time; seasonably. 

adj
  • Near the start or beginning. 

  • Near the start of the day. 

  • Having begun to occur; in its early stages. 

  • At a time in advance of the usual or expected event. 

  • Arriving a time before expected; sooner than on time. 

  • Of a star or class of stars, hotter than the sun. 

oh dark hundred

noun
  • Some unspecified hour in the early morning (implies an unpleasant time to be awake) 

How often have the words early and oh dark hundred occurred in a corpus of books? (source: Google Ngram Viewer )