This was covered in another thread awhile ago:
http://duc.digidesign.com/showthread...ight=quicktime
But I think all you need to do is the following:
"The delay was fixed by setting Sound playback out of the computer's line out. This of course disables the ability to use Digi hardware for non-PT playback (like iTunes), which is a drag. It would be REALLY great to get this fixed."
Digi allows PT hardware to serve as an interface for non-Digi apps (like iTunes), but this does not work well with Quicktime. Disable this feature and you should get immediate playback. You can always toggle it on if you want to listen through your hardware, but I just leave it off.
Best,
Jamshied