halcyon days vs yestertime

halcyon days

noun
  • A period of calm, usually in the past and often nostalgic. 

  • Period of calm during the winter, when storms do not occur. 

yestertime

noun
  • Time previous to the present; the past. 

adv
  • In times past, at a prior time; in the past. 

How often have the words halcyon days and yestertime occurred in a corpus of books? (source: Google Ngram Viewer )