Backup Specific days monthly SQL Server
This will be tough to do with the built-in schedule UI, unless you want to create 12 different schedules, but you can easily build this into your job step. Assuming it runs every night:

IF DAY(GETDATE()) &lt;= 8 OR DAY(GETDATE()) &gt;= 28
BEGIN
  -- do backups
END


On other days (9th -> 27th), the job will still run, but everything inside the IF conditional will not. So other than having an entry in sysjobhistory, it will be as if it didn't run at all.

Another idea would be to have a different job that runs every morning, checks the date in a similar way, then enables / disables the backup job accordingly. Or similarly with two schedules (one on the 9th to disable, and one on the 28th to enable).