Hi Sgtbilko,
Backup job can be targeted to specific partitions. You can schedule the Backup job as per your requirement and select particular partition ( Backup Job Properties | Device and Media | Device).
When robotic library partitions are configured, VERITAS Backup Exec creates a drive pool for each partition. Jobs targeted to a partition drive pool run on the media located in the partition's slots.
Refer the following TechNote's for reference :
http://seer.support.veritas.com/docs/206843.htm
http://support.veritas.com/docs/241773
http://support.veritas.com/docs/241773