Currently there are only two summary display options for Date and DateTime fields. Those are "Earliest" and "Latest." When grouping Tasks by a particular criteria (say the Link) you can see either the earliest Start Date for all the Tasks belonging to an Asset or Shot, or the latest End Date. The proposal here is for a 3rd option to show a summary range which would display the range over which all the Tasks Start/End dates fell (e.g. 01/01/2013 - 06/01/2013). This way it would be easier to see the full breadth of time for particular fields.
Add Range as a Date Field Summary Option