What is Additional/Alternative NTP server section used for?

Mushroom network devices synchronize time with external public NTP servers e.g pool.ntp.org.

Primary use of adding an additional NTP servers is when you have a private/MPLS network and the public NTP servers (e.g. pool.ntp.org) are not reachable. This can be done by clicking on “Add” in the additional NTP server section (under the ‘Advanced’ tab) and providing the internal/private NTP server IP address and clicking ‘Apply’ as below: