Hi there.
The
online help explains how to create Web Access rules which is what you would typically use to do something like you require. In short you need to do the following
Ensure the users are going through a WinGate proxy server either by intercepting the connection or typically, by setting their browser proxy settings.
Create a WebAccess rule
Set WHO to their user
Set WHAT to be the site facebook.com or match on a data list with facebook in it
Set WHEN to be the time you want the rule to apply for
Let us know if you need any more help
Thanks
Aaron