JAVA J2EE 4 U

 SELECT 

    ROUND(AVG((END_TIME - START_TIME) * 24 * 60), 2) AS avg_completion_time_minutes

FROM 

    V$RMAN_BACKUP_JOB_DETAILS

WHERE 

    START_TIME IS NOT NULL

    AND END_TIME IS NOT NULL

    AND STATUS = 'COMPLETED'

    AND BACKUP_TYPE = 'INCREMENTAL';