You can set an execution schedule for the Network Shell Script Job on the Schedules tab in the job editor, when you open the BSA Recommended Database Cleanup Job.
You can schedule the job so it can run one time, recur hourly, daily, weekly, or monthly, or recur at some arbitrary interval, whichever time frame works best for your data cleanup strategy.
BMC recommends that you schedule the cleanup script to run once a day using the execution mode of TYPICAL. If once a day is too frequent, use INDIVIDUAL mode to clean up the database and file server at least once per week.
You should also plan to run the script after a month in INDIVIDUAL mode, and to clean the agent, Application Server caches, and the repeater.
For a complete description of options, see Network Shell Script Job - Schedules.