Indicates a maximum time interval, in minutes, hours, days, or months, for alarm data on the backup table until it is discarded, regardless of the time data remains on the main table. For example, to keep data for 24 months on the main table and six more months on the backup table, this option's value must be 30 months. This property works with the BackupDiscardTimeUnit property. Default value is 12 (twelve time units indicated by the BackupDiscardTimeUnit property).