Setting Discussion Forum Deadlines

From your course homepage, select the desired discussion forum.
From the Administration block, select 'Edit settings.'
Click to expand the 'Restrict access' pane.
Click 'Add restriction.'
From the available options, select 'Date.'
Adjust the 'From' date as desired. (This will prevent students from accessing the forum before the specified 'From' date.)
To set a closing due date for the forum, click 'Add restriction' and select 'Date' again.
From the 'Date' dropdown menu, select 'Until' and adjust the end date as desired. (This will prevent students from accessing the forum after the specified 'Until' date.)
Save your changes by selecting 'Save and return to course' or 'Save and display.'