rag week vs time of the month

rag week

noun
  • The days of the month when a woman has her period. 

  • An annual event in many universities where students engage in unusual activities to raise money for charity. 

time of the month

noun
  • Synonym of menstruation: the monthly period during which a fertile woman menstruates. 

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