Configure Forefront Scheduled Scan by GPO

Remember this will only work on Windows 2008 onwards since it requires the GPO preferences technology (formally known as 'Policy Maker').

The key that determines which day the scan runs in:

HKLM\Software\Policies\Microsoft\Microsoft Forefront\Client Security\1.0\AM\Scan

REG_DWORD ScheduleDay

1 - Sunday
2 - Monday etc.

Also

HKLM\Software\Policies\Microsoft\Microsoft Forefront\Client Security\1.0\AM\Scan

REG_DWORD ScheduleTime

Denotes the time of the scan in minutes passed midnight.

Cheers!