You mean you've got a descending DATE sort?
Using divider option in Alpha sort mode is simple -- it divides into sections for each letter.
Using divider option in Date sort mode is more interesting. It basically groups the first group into files within an hour from each other, next group within a day of each other, next group within a week, next groups within a month. Enable the timestamp option to see the actual dates for the files/folders so you can better understand.