Imagine a long list of websites that you can either allow or block from your internet. The user can go down the list and block every single one relatively quickly, however on the backend each of these websites can take anywhere from 5 seconds to 1 minute. This can build up quickly if, say, 30 websites blocked at the max time of 1 min each, it could take 30 mins. The user is not stuck on the page and they are free to do whatever they please on the app. Is there any clear way to indicate to the user that their change is not immediately ready? I thought about adding a small tooltip/popup saying "changes are being added...", but is there a drawback because the user is not forced to go on the screen, they won't see when it is completed?
Assuming, block/unblock are the only actions there for list items:
I think you need to add disable class (may be only the gray font color) on that item on the list which has been acted upon by user. Then you can add a tooltip for them.
Once, user is used to reading a tooltip, it will be actually easy for him/her to recognize the acted links and wait.
Keep a short and simple tooltip: Blocking... or Unblocking...
And after action is finished, change the state of the item.