resetting network time

hello,

I am trying to get my Apple TV working ----it gives me 'Account Sign-in Failed" message and says it can't sign in to the iTunes Store until the network time has been set. Please try later. This is frustrating and we have tried several times to get this to work-------where do we "re-set" the network time??? Can't find it anywhere on the menu, general settings etc.

thank you!