Q: Why Apple tv cant set date and time?

Morning Taninha,

Thanks for using Apple Support Communities.

TCP port 123 is used to communicate with a network time server.

If your router is blocking this port it will never set the time.

For more information on this, take a look at this article:

Apple TV: TCP and UDP ports and protocols used

http://support.apple.com/kb/ht2463

Also it needs an active internet connection.

Apple TV (2nd and 3rd generation): Troubleshooting Wi-Fi networks and connections

http://support.apple.com/kb/TS4546

Best of luck,

Mario