code: public void setDefaultDelay(long delay, TimeUnit unit) {
          if (delay < 0) {
              throw new IllegalArgumentException("Parameter delay must be greater or equal to zero.");
          }
          if (unit == null) {
              throw new IllegalArgumentException("Parameter unit must not be null.");
          }
          this.defaultDelayInMs = unit.toMillis(delay);
      }
docs: Sets the default required delay when executing/submitting tasks.
  <p>
  Default value is zero, no required delay.
  
  @param delay the value delay
  @param unit the time unit of delay
  @throws IllegalArgumentException if {@code defaultDelayInMs} is negative.
  @see #execute(Runnable)
  @see #submit(Callable)
  @see #submit(Runnable)
  @see #submit(Runnable, Object)
  @see #setIncrementalDefaultDelay(boolean)