Main NTP server will synchronize its time from public NTP servers.
This article will help you to Setup time synchronization (NTP) server on Artica systems.
Now you need to set up local NTP server to synchronize their time from public NTP server.
Go to Your System / Time Server using the left menu.
You can choose ntp family as per your choice or location using “Default NTP Servers” dropdown list.
NTP server uses UDP port 123 for service requests.
So you need to open port 123 in the firewall.