Setting the AV to update at user defined intervals can be indirectly achieved, but it would be better if it was built into CIS.
Open CIS and click ANTIVIRUS → SCANNER SETTINGS
On the REAL TIME SCANNING tab, disable AUTOMATICALLY UPDATE VIRUS DATABASE BEFORE SCANNING.
On the MANUAL SCANNING tab, disable AUTOMATICALLY UPDATE VIRUS DATABASE BEFORE SCANNING.
On the SCHEDULED SCANNING tab, enable AUTOMATICALLY UPDATE VIRUS DATABASE BEFORE SCANNING and disable SHOW SCANNING PROGRESS
On the SCHEDULED SCANNING tab, disable SHOW SCANNING PROGRESS
Set up a series of scheduled scans that only scans a single innocuous file (e.g. a shortcut on your desktop) with a regularity that suits you and your environment.
I currently use this method with a series of scheduled scans set to scan a single desktop shortcut at 4AM, 8AM, 12AM, 4PM, 8PM and 12PM.
Yes, this is a workaround, but, equally, yes it works.