Sales stage audit in a report format?

Is there a way to report on activity that hasn't happened for a certain time period? 

Specifically, what I'm being asked to do is figure out how to get an exception report based on information in the Audit log - i.e. If a sales stage has not moved for a certain period of time.   We are able to look at this information at a line item level in the Audit Log, but the sales manager wants to get a report of all line items that are 30 days dormant, 60 days, 90, etc. specific to each Sales Stage.  I haven't been able to find the "date changed" for Sales Stages in the reporting module, much less how to report on a lack of action taking place.