When setting up your board initially, you will see an option to set a "Board End Date". If at any point you wish to change this end date, the setting can also be found and changed in the Settings -> Basics menu.
Upon reaching the date entered in this field, your board's automatic notifications being sent, as well as the grade passback connection to your LMS will end.
This field can also be left blank if you wish for the board to continue functioning in the same way.
*Note: If you intend to enter grades manually, do so AFTER the board's selected end date. Automatic grade-sync will overwrite entered grades, otherwise.