When setting up your points scheme, you will see an option to set a "Grading End Date." Upon reaching the date entered in this field, the grade passback connection to your LMS will end and your board's automatic notifications will stop being sent.*
If at any point you wish to change this end date, the setting can also be found and changed in Settings → Points. While you are welcome to push back the end date as many times as you need to, you must always have a specified end date; it cannot be open-ended.
* Note: If you intend to edit Yellowdig grades for students manually, you will need to do so AFTER the board's selected end date. If you do not, automatic grade-sync will overwrite any manually entered or edited grades. An additional option to prevent overwriting by the grade sync would be to export the Yellowdig grades, edit them as you wish, and then reimport them into a new assignment in your LMS that is not linked to Yellowdig.