Representing durations as long's is very error prone. We've seen (and fixed) hundreds of unit mismatch bugs inside of Google.

We (Guava) have recently updated most of our public APIs to add java.time.Duration-based overloads. Caffeine and Selenium have done so as well.

Basically, I'd like to see the following APIs added:
Mockito.after(java.time.Duration)
Mockito.timeout(java.time.Duration)

And ideally the long-accepting APIs would be deprecated.