Any way to get Software Update to run in the background at a specified time of the day?

G'day.

Is there any way to get Software Update to run in the background at a
specified time of the day? I don't want to be bothered with any
notifications unless there actually are updates to download, i.e. as it
does when set to check automatically, but I want to control the time of
day.

I can control the time of day by using iCal to launch a script, e.g:

     tell application "Software Update"
          run
     end tell

But I don't know how to prevent Software update from bothering me unless
there actually is an update.

TIA,
 Jamie Kahn Genet

-- 
If you're not part of the solution, you're part of the precipitate.