Studies have shown that human hearing cannot really tell the difference between 2 sound sources that fire less than about 5 mSec apart. At the speed of sound this means you can be off about 4 feet in the settings with little problems.
What is more important is level adjusting or calibrating the speaker levels. (you dont sit the same distance from all the speakers so some will naturally be louder than others).
Our
Primer & FAQ has an article called "Home Theater Means Accuracy & Calibration!" that will explain all this.
Hope this helps.