Backup set Retention

Hi,

    I have Symantec Backup exec v-ray edition in media server. I have made a schedule Monday backup of VM machine to NAS at every Monday 11:00pm, in opinion of set keep 7 days and job completed at Tuesday around 03:00am. When one week past, backup job cycle will start 11:00pm, but media server will delete Monday backup set around 02:00am and job will stop by Symantec backup. Then I have change to keep 154 hours but retention time is not accurate before 11:00pm. How to solve or make retention to manual?

Regards,

YM user