[detaro]

Yes, they clearly say that they use atomic clocks in addition, but that's commercially available as well. Atomic clock for frequency stability short- to mid-term, GPS to keep it synced to global time. E.g. in many cases, mobile-phone base stations contain just such a setup, and the data-center versions should fit in a few HE.

[stuckagain]

And then all you need is a team of 12 full time SREs to manage it.

[detaro]

A system build on top of it? Possibly, but thats the trade-off if you don't want to pay for/be lock-in to somebody else running it. For just the timing stuff: not really. Of course it adds complexity, but these things are established and should be quite stable.