When you add a restriction to a record, it takes effect immediately. When you remove a restriction, it becomes effective at midnight on the given end date of the restriction.
If a worker is working on a record when a restriction is added, the system doesn’t remove them from the record. However, it prevents them from taking further actions. For instance, if they are in the middle of completing a workstep, they remain in the workstep but will encounter an error if they try to save the workstep.
We would not expect this to be a common occurrence, as we would expect in most cases that workers on the case would be made aware of restrictions or wouldn't be in the process of working on those cases at the time of the restriction.