Set the casting time for the heroes to 0 too. It's in the unit tab.
Art - Animation - Cast Backswing (Real)
The amount of time it takes a unit/building/hero to go through half the physical movement necessary to cast a spell. If the unit/building/hero has no animations for casting spells, the time set in this field still applies, but there will be no viewed physical movement. This field combines additively with "Art - Animation - Cast Point" to form the total time taken to physically cast a spell.
Art - Animation - Cast Point (Real)
The amount of time it takes a unit/building/hero to go through half the physical movement necessary to cast a spell. If the unit/building/hero has no animations for casting spells, the time set in this field still applies, but there will be no viewed physical movement. This field combines additively with "Art - Animation - Cast Backswing" to form the total time taken to physically cast a spell.