See CockroachDB’s Living Without Atomic Clocks [0]. TrueTime [1] is a proprietary Google technology. Considering TrueTime upper bound uncertainty (< 10ms) [2], it may depend on Google’s network quality and breadth.

[0] https://www.cockroachlabs.com/blog/living-without-atomic-clo...

[1] https://cloud.google.com/spanner/docs/true-time-external-con...

[2] https://static.googleusercontent.com/media/research.google.c...

CockroachDB assumes you use NTP on your servers — but if you actually put GPS clocks into your servers, you could adjust the safety interval it assumes for clock drift down, and it'd behave pretty much the same as Google's.