Why is my (automatic) clock running 8 minutes behind?
This might help.

How can I tell if my Mac is keeping the clock updated properly?
And, this
ntpd: consistently incorrect time on mid-2013 MacBook Air

TL;DR:  open a command prompt, aka Shell, aka "Terminal". 

What's the output of 'ntpq -p'?
What is in /var/db/ntp.drift ?

A list of servers is available at http://support.ntp.org/servers; you have to try to select the servers that are close to you, especially not just geographically, but network-wise.