This 'report' is actually at tool that lets you edit all the dates for all]
the activities in your course on a single page.

You can install it from the Moodle plugins database
http://moodle.org/plugins/view.php?plugin=report_editdates

Alternatively, you can install it using git. In the top-level folder of your
Moodle install, type the command:
git clone git://github.com/moodleou/moodle-report_editdates.git report/editdates

Then visit the admin screen to allow the install to complete.

Once the plugin is installed, you can access the functionality by going to
Reports -> Dates in the navigation block when you are looking at the course.