Network Timing Protocol (NTP)

Utilize NTP Service in Rutgers:

Local Unreferrenced NTP server for LAN sync purpose

You may suggest there is nothing wrong with a SNTP subnet of clients and
servers which is wholly contained and where synchronization is never
leaked to the NTP subnet. I have no problem with this should it be
practical."

In other words, it is okay to have a non-referenced NTP server, as long as
it is strictly for personal use and you are very careful to keep it that
way.  If you are not connected to the internet at all, then there is no
problem with doing this.

The real danger is having non-referenced or substandard clocks open for
public access, since this would ruin the quality of the NTP algorithms.

I personally use a Linux machine as a masquerading router and firewall,
behind which is a private subnet.  The front end machine syncs to a
reference clock on the internet and acts as NTP server for the private
subnet, however my NTP service is firewalled to prevent public access. 
When the front end machine is disconnected from the internet, the subnet
stays in sync (in that all machines will drift identically).

There are significant advantanges to running your own NTP server in this
manner.  The quality of NTP sync is dependent on the quality of the
network connection to the reference clock.  The sync to the remote clock
is probably accurate within 10 msec, but the sync between the local
machines can be easily less than 1 msec, due to the small 100bt network.