Sending Message in Active Directory to all domain Users? ....Anyone?

Question

I have a situation and I’m hoping someone can help? I am going to implement a password change across our domain on Jun 1st. But, I want to send a message to all domain users a few weeks before like a warning that this will happen on this day, before they login. I created a group policy drilled down to the Security Settings, Local Policy, Interactive Login, Message Title for Users Attempting to Logon, Typed in my message and I put that GP on my Departments OU to test it but it never showed up on my Depts PCs after rebooting. I also ran a gpupdate /force then restarted but still no message. Am I doing something wrong?Also the Computers are waiting for Network when they startup. Help....