1. Add a property named "Last Modify Date" and apply to all cards, e.g. Story, Task, Defect
2. Make the property hidden
3. In every transition, add a new filed which the "Last Modify Date" will be changed to "Today"
4. Add a query on the wiki page as follow
Comment: It would be much easier if Mingle can expose the "Updated_At" property from the Rails ActiveRecord API...