johnt
You can create a domain in server manager Domain panel, eg facebook.com which resolves using the local DNS option (rather than Internet DNS servers) & points at your servers main (local) web site, so if users try to access facebook.com they get your main website.
You can create a cron job to issue a db command that will configure the "redirected" domain(s), & schedule that for 2pm.
You can create another cron job to issue another db command that deletes the redirected domain(s), & schedule that for 12 midday.
To get the appropriate command, create a domain in the Domains panel in server mananger, & then review the messages log file.
I do something similar in Dansguardian & it works fine.