How is Person Time and Reviewer Time Calculated?

We are in the process of trying to convince our management to migrate away from manual metrics and more towards automation.  One of those metrics is review time.  We currently maintain a spreadsheet for each inspection where inspectors enter their review time manually.  Some of us would prefer to just use the time calculated by CoCo. 

Can anyone tell me how those metrics are calculated?  It's obviously not the time the review is open in a browser.

Thanks.

- Dave