This is a function of SUS. The reason for having the No-button disabled is because end-users shouldn't be able to postpone it. Otherwise, some users will continue to postpone the updates and your machines will not receive their patches. As a best practice, just have your users log off before they leave work and schedule the installs at night. Configure SUS to automatically reboot the computers. When the users come back into work, you environment will be patched and there will be no interruption for the users.
This was first published in December 2003