How Do I Add or Create a Lock Date to a Discussion Board?
Lock dates can be used to restrict a students ability to contribute to the discussion thread. A student will have view access, but will be unable to contribute to a discussion thread that is locked.
Inside of your course, click on the Discussions tab at the top of your page.
Click the drop-down next to the topic and click Edit Topic.
Edit Locking Options
Under Locking Options, select Unlock topic for a specific date range and check the first two boxes. Customize the dates in the boxes for the start date and end date. When finished, Save and Close.