UTC is monotonic, even during leap seconds. (A positive leap second adds a 23:59:60; no timestamp ever repeats, the clock never moves backwards.) (Negative lea

UTC is monotonic, even during leap seconds. (A positive leap second adds a 23:59:60; no timestamp ever repeats, the clock never moves backwards.) (Negative leap seconds are similar, and do not affect the monotonic property.) POSIX/Unix timestamps, however, are non-monotonic. But that's a different timescale.