Kia ora,
The easiest might be to set up a run once policy that executes the following command to schedule the running of the softwareupdate command.
/usr/local/bin/jamf scheduleTask -command "/usr/local/bin/jamf runSoftwareUpdate -randomDelaySeconds 600" -name "ScheduledUpdate" -day 5 -hour 11 -minute 5
This will setup a launchd plist in /Library/LaunchDaemons that will cause the computer to run softwareupdate as scheduled. In the above example, on the 5th day of the month within 10 minutes of 11:05am (or within 10 minute of the next time to computer starts/wakes up). The 10 minute window is so the software update server won't get hammered.
