man day vs working day

man day

noun
  • The amount of work that one person can complete in one day, often considered to be equivalent to eight man hours 

working day

noun
  • The part of a day in which work is done; the number of hours one must work per day for a specified wage. 

  • Any of those days of a week on which work is done, officially Monday to Friday in many countries (even though many people work on weekends). 

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