oh dark hundred vs oh dark thirty

oh dark hundred

noun

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

oh dark thirty

noun

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

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