This is not a new idea - it's to do with using a feature that is not yet functioning as expected.
To change a class's settings of Start Date, End Date, etc., the Help FAQ "Edit Course Info" instructs:
1. Begin at the Netspace Home Page and click on the Class name, under "Teach".
2. Then click on "Settings" and on that Settings page, click "Edit Course Details".
3. However, nothing is editable, so I guess the web team would wish to rectify and enable this feature here.

Our Help Chat line came in handy here - Francine F. instructed me to click on the cog icon alongside the class name (not the class name itself), on the "Teach" tab on the home page.
This takes you to the enrolment and class info page. Clicking on the cog icon alongside the info section then takes you to the class settings editing page, which is... editable! Problem solved! This certainly merits a great 'Thank you' note to Francine F.! Good work!