@DoNotStrip
  default long now() {
    return TimeUnit.NANOSECONDS.toMillis(nowNanos());
  }
Produce a timestamp. Values returned from this method may only be compared to other values
returned from this clock in this process. They have no meaning outside of this process and
should not be written to disk. This method uses the same timesource as {@link #nowNanos()}

<p>The difference between two timestamps is an interval, in milliseconds.

@return A timestamp for the current time, in milliseconds.
fbcore/src/main/java/com/facebook/common/time/MonotonicClock.java