How to get time from a custom SNTP port?

I am experimenting with simple and easy (hopefully) and there’s an Android app called Time Server that can get great GPS time at Stratum1, but it runs SNTP:1234

What NTP server/service can take this and make it usable on the local network?

I think I can port forward 123 to 1234 for an external pool, but want to log statistics for stability/validation.

Ntpd/q queries won’t go outside of NTP:123 or they make it really hard to do so?
How does polling SNTP work in this use-case?

Normally servers run on port 123.

For what it’s worth, Chrony has a port option. I haven’t used it, but you should be able to do something like:

server port 1234