If you ever want to have an NTP server in environment where there is no internet access, you can run ntp server on Linux with the following configuration.
# sudo vi /etc/ntp.conf……server 127.127.1.1fudge 127.127.1.1 stratum 12……
# sudo /etc/init.d/ntp restart
Run ntpq to check the local stratum level. (You can change it to any other level, it doesn’t have to be 12 as shown above)
# sudo ntpd –q
You will also have to adjust the ACL using “restrict” configuration. (In this case, allow NTP server to be accessible from 192.168.1.0/24)
Another Ref: https://help.ubuntu.com/lts/serverguide/NTP.html