Wonder why your updates that were approved in SUS are not applying to your client PC's at the scheduled time? If your PC's are not setup with a Local Admin account the update will be transparent. Take a look at the event viewer on the day the updates were planned for release. You will see an event #18 - Automatic updates. Check the event viewer the next day. You should see and event #4377 - NT Service Pack. This is the installation after the next user reboot.
If the user is a local admin a pop up box will alert the user that a update is ready and prompts the user for installation (depending upon GPO options)