NIST Internet Time Servers

One really wants one’s local systems (on any sort of significant network) to use timing that is identical – or as close as humanly possible. This is accomplished by using a reference server that is the holder of the always true time (if this clock should get off by a few minutes, then the whole network will). You can pay for access to these servers, but the National Institute of Standards and Technology (NIST) makes its NTP servers publicly available.

My recommendation – configure one (or preferably more) servers on your network to receive their time from the NIST’s NTP servers and then make those servers NTP servers that the rest of your network communicates with.