There is a difference between blocking and parrying. According to some sources, parrying can be done when the guard hasn't completely been changed, or it can be done mid animation if that makes more sense. Blocking however, does only work when the guardswitch animation has finished. So parrying should be the same for all heroes, however blocking has different speeds. The warden can change his guardstance much quicker than the lawbringer. If you want the exact frame data, the warden changes his guard within seven frames, while the lawbringer does it within 22 frames, which makes quite the difference.