under the parental control, whether you have entered some URLs? this function is used for allowing some MAC addresses to access some URLs under appointed time.
so if you didn't enter any URLs, maybe you can't access to any website.
that's my own opinion, for your reference.

As far as i can make out the conditions for parental control are
chosen MAC address can access the chosen URLs during the chosen times. (logic AND conditions)
Way to limiting, unless the kids only visit a handful of websites.
It would be far better to have a wildcard "www.*.*" approach so all websites are allowed/disabled during the preset times.
Failing that i will have to enter every URL in existence, which may take some time!

Maybe someone else has a better work-around solution?

So how would i block xbox live?

"So how would i block xbox live?"
You can find out the port numbers of Xbox live and the MAC address of Xbox. And then go the web page of the modem, enble IPV4 firewall and do filtering rules based on the MAC address of Xbox and port numbers to block the connnection on the Xbox.