How to track untouched leads?

How to track untouched leads?

Hi there!

I'm working on a project and I need your help...
Here is our process:
  1. When a lead is generated, the marketing team work on the qualification. Based on the info we retrieve, the lead status is updated from "To Qualify" (default value) to "MQL" or "Not Qualified"
  2. These information are used to assign the lead to a sales rep. For instance if the lead is MQL and country is France > Assign lead to John

  3. When the lead is assigned it triggers a notification to John, and to his manager.
Now what I want to build is alerts (reporting or dashboards) of leads unmanaged by John.
For instance, 36 hours without any activity (no note, no call, no email) and activity owner is John. 
I intended to use advanced filters untouched records but I'm struggling.

Any clue?