If you've tried to control when Shatter shatters, you may have shattered your computer in frustration. Here's the trick ( assuming you want to delay the shatter until two seconds into your comp):
With the Current Time Indicator at the start of the Timeline, turn the stopwatches on for Radius (in the Force 1 parameter category) and Gravity (in the Physics category). Set both properties to zero.
At two seconds, set another Radius keyframe, also at zero, and another Gravity keyframe, also at zero.
Press the Page Down key to move forward one frame and set Radius to its default, .40 and Gravity at its default, 3.00.