At a previous role, we needed nanosecond precision for a simulcast radio communications system. This was to allow for wider transmission for public safety radio systems without having to configure trunking. We could even adjust the delay in nanoseconds to move the deadzones away from inhabited areas.

We solved this by having GPS clocks at each tower as well as having the app servers NTP with each other. The latter burned me once due to some very dumb ARP stuff, but that's a story for another day.