because if the shout was to take as long as in the trailer you cant use the full shout in quick reflex situations? Just a thought.
The overall length wasn't changed. The gap between Fus and Roh was lengthened, and the gap between Roh and Dah was shortened. My guess is that getting to Roh so quickly was causing balance issues.
Either that, or the sound file in the trailer was simply a placeholder.