Hi rk06,
Displaying notification on the reason code change is not a big task and can be quickly implemented. The second part of the request is a little bit complicated but is possible to be done.
I think that you will not able to do it using the Cisco Finesse Toaster Notification API (Finesse.ClientServices.Toaster) as it is not designed to be auto close. More about how this API works you can find here: https://gaman-gt.com/articles/cisco_finesse_notification.html
A good idea would be to use the browser notification API but it has some limitations. What is also interesting, they relay on browser on OS setting. This is something that you can also find in the page mentioned above.
Finally, here is a sample gadget, that may help you to try different setting for the notifications that works on the reason code change. You can change the notification basic (use Finesse or Browser API). The gadget can be downloaded from here: https://gaman-gt.com/downloads/finesse_gadgets/Finesse_Notification_Gadget_on_Reason_Code_Change_2019_12_30.zip
Hope that helps you.