A database backup requires an Application Backup schedule. You cannot perform backups if this type of schedule is not included in the policy. The database agent automatically creates this schedule and names it .
The backup window for an Application Backup schedule must encompass the time period during which all scheduled jobs and unscheduled jobs can occur. This window is necessary because the Application Backup schedule starts the processes that are required for all database backups, including those started automatically. You can choose to set the window for the Application Backup schedule for 24 hours per day, seven days per week. This window ensures that your operations are never locked out due to the Application Backup schedule.
For any policies that are used for SQL Server 2005 or later read-only filegroups, consider creating a schedule with a retention level set to infinity. This level can enable you to avoid redundant backups.
More Information