What is the model number of your router that might help ?
lookup the ntp server for your location and dont use http://ntp
blaa bla bla use the ip number of the server you may also have to pick a server that uses the old style of sending the time info to your router
If it's an old router you might not have the option to change the date past 2012
that's why I suggested you might have to telnet into your router, it's not that hard to change the date if its an open source Linux running busy box which I think a lot of buffalo routers use