For serializability, all you care about it is some sequential order. You get that with hybrid logical clocks (http://www.cse.buffalo.edu/tech-reports/2014-04.pdf). It gives you a monotonically increasing timestamp that you can use instead of dumb version numbers.
On the other hand, if you want to ensure linearizability, you do care about the worst case clock drift, which in CockroachDB is a configurable parameter. One can adopt Google's Spanner's approach ("commit wait"), which is to wait out the response to the client to ride out NTP uncertainty (typically a few milliseconds inside a data center, but 100s of milliseconds in the wide area).
On the other hand, if you want to ensure linearizability, you do care about the worst case clock drift, which in CockroachDB is a configurable parameter. One can adopt Google's Spanner's approach ("commit wait"), which is to wait out the response to the client to ride out NTP uncertainty (typically a few milliseconds inside a data center, but 100s of milliseconds in the wide area).