It is also important to realize that an atomic clock will only give you a steady pulse. It will count seconds for you, and do so very accurately, but that is not the same as knowing what time it is.

If you get a rubidium clock for your garage, you can sync it up with GPS to get an accurate-enough clock for your hobby NTP project, but large research institutions and their expensive contraptions are more elaborate to set up.

There are dedicated turnkey vendors these days, so there's no need to get elaborate. All you need is a U of rack or two and enough cash.

Example: https://www.accubeat.com/ntp-ptp-time-servers