What is the origin of the idiom "month of Sundays" and when to use it?

The idiom "month of Sundays" gained popularity in the United States during the 19th century and later on spread to other English-speaking regions. Its origin lies in the combination of the words "month" and "Sundays," with "month" representing a long period of time and "Sundays" symbolizing rest or leisure. It is often used when talking about situations where time feels like it's going very slowly, like waiting for something or doing a boring.