As Mr. Paul put it:
daterange provides documents that have been modified in the given interval. Unfortunately, Google requires that dates be entered in Julian format, e.g. charter scc daterange:2451193-2455757. Click here for a Julian date converter.
How is this useful for legal research? When you have a inexact facts that you need to verify. Perhaps you want to find information about a motor vehicle accident in Edmonton in January of 2009. Try this Google search:
accident edmonton daterange:2454832-2454862
The search will net you news stories, YouTube videos, and other interesting results.
CNET offers further details about date range searching with Google.
Can you think of other useful date range search scenarios?