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...