What does "a month of Sundays" mean?
A long unspecified period http://www.collinsdictionary.com/dictionary/english/a-month-of-sundays
A lunar or Solar month.
I'm not sure. Where did you hear that?
30-31 sundays or, about 30-31 weeks. It is a colloquialism used by us old folks, as in " ain't seen you in a month of sundays".
It's a long time...
Around a half year.