To prevent NTP amplification attacks, NTP is blocked at the network edge inbound. Inbound requests on the NTP UDP port are blocked. While outbound requests are allowed, most implementations of the NTP protocol require communication with the inbound port as well, which is indistinguishable from a blind port access attempt.
You can access Neural's NTP servers via ntp.neural.net.au - individual server addresses are provided in the appropriate article in this knowledge base. Configuration examples are also provided.