code: public final Timeout deadline(long duration, TimeUnit unit) {
      if (duration <= 0) throw new IllegalArgumentException("duration <= 0: " + duration);
      if (unit == null) throw new IllegalArgumentException("unit == null");
      return deadlineNanoTime(System.nanoTime() + unit.toNanos(duration));
    }
docs: Set a deadline of now plus {@code duration} time.