In the Supply Planning Workbench (part of MRP feature), we have an Action that says "Consider Firming proposed Planned PO No. 4204 as it is nearing its time-fence threshold." which we don't understand why and when such a kind of Action ("Time Fence Threshold") is triggered. Our Supply Plan Definition Horizon Start Date is 12/1 and the item's Time Planning Fence is 5 days which means that no suggestion of new supply orders or rescheduling in and out or cancelling of supply orders until 12/5. Therefore, the earliest suggested supply order date is 12/6. I guess we don't understand what "time-fence threshold" means either.