Hello @jmjones,
Have you seen this previous reply from @sitloongs where he covers the “Service Forwarding” settings for NTP traffic?
This post from @MartinLangmaid has some helpful insights too
You do not need to declare the DHCP option 42 (time server option) with this setup.
Where possible, we always use the GPS antenna as primary for time reference; the secondary comes from a local NTP approved server or the local pool at ntp.org (find your local, i.e. au.pool.ntp.org)
Happy to Help,
Marcus