This policy setting allows you to set the number of hourly versions not to prune after Days Back. With a 2016 format notebook, OneNote will automatically store previous versions of the pages in the notebook, and it will also store a recycle bin for all of the deleted pages and sections.
If you enable this policy setting, you may specify the number of days to keep hourly versions after the Days Back setting. This value specifies the number of days past "DaysOfAllVersions" to keep hourly version history information. Users will keep one version per hour for this number of days after "DaysOfAllVersions".
If you disable or do not configure this policy setting, OneNote will keep hourly versions for the past 5 days.