Time.MonoMonotonic clocks.
Monotonic clocks are unaffected by corrections to the real-time clock, and so are a better choice for timeouts or measuring intervals, where the absolute time doesn't matter.
A monotonic clock may or may not include time while the computer is suspended.
val sleep : _ t -> float -> unitsleep t d waits for d seconds.
val sleep_span : _ t -> Mtime.span -> unitsleep_span t d waits for duration d.