code: @Override
      public AnimatorSet setDuration(long duration) {
          if (duration < 0) {
              throw new IllegalArgumentException("duration must be a value of zero or greater");
          }
          for (Node node : mNodes) {
              // TODO: don't set the duration of the timing-only nodes created by AnimatorSet to
              // insert "play-after" delays
              node.animation.setDuration(duration);
          }
          mDuration = duration;
          return this;
      }
docs: Sets the length of each of the current child animations of this AnimatorSet. By default,
  each child animation will use its own duration. If the duration is set on the AnimatorSet,
  then each child animation inherits this duration.
  
  @param duration The length of the animation, in milliseconds, of each of the child
  animations of this AnimatorSet.