Doing some extrapolating from logic and looking at some of the churches’ web sites, it appears that some churches have a special service when there is a fifth Sunday in the month which is comprised mainly of hymn singing. These appear to be largely Southern Baptist churches.

“Join us for a Fifth Sunday Singing at 5:30 on May 31. There will be a time of fellowship, followed by prayer and finally an old-fashioned hymn sing.”

Source

Ah! @janbb that makes all sorts of sense! I could only think of that expression in English, ‘A month of Sundays’.... but I knew that wasn’t helpful. ( I’m also not sure what that means, either. )

People used to live far apart from each other on the frontier, and usually only saw each other when it was Sunday. They would all haul into town for church. In good weather, it was often made a day, with many gathering after church to picnic, socialize, and watch the preacher dunk sinners in the river and proclaim them new. A month of Sundays is just going to church a few times without having seen that person.
Imagine how would it would have been like if they invented cell phones back then!”

Interestingly enough, there are four “fifth Sundays” in most years.

A Month of Sundays actually means a very long time. If it takes a week to get from one Sunday to the other, what if every day of the month was Sunday…it refers to many weeks, or months, or possibly even years.