URL Blocking Alias not going in

[4o4rh]

I have an urgent need to block urls to stop the kids from being distracted during school hours e.g. youtube.

my idea was to setup a firewall blocking rule with a url alias for the sites that need to be blocked and create a schedule to block during school hours.

when i try to add entries to the url alias
e.g. www.youtube.com or https://youtube.com it says a url must be entered and loses the settings i.e. the alias name, description, etc.

what am i doing wrong?