Uncheck the auto-set, close Sys Prefs. Then re-open them, and recheck the auto checkbox.
Also, beside the Date/Time checkbox, is the timeserver. Choose the one for your continent. Or try a different one, as someone in between (your ISP?) may be blocking the suspicious timeserver.
If that still doesn't work, trash com.apple.systempreferences.plist, and check to see if someone is blocking UDP port 123. A custom local firewall rule on your system, your firewall router, your workplace, your ISP.