Although Excel can't track editing time, here's an idea.
In Microsoft Outlook, one can track Office documents thru the Journal.
I believe the "Duration" field is the time the document was opened, which is
different than the time the document was edited.
Here's a technique from within the Journal.  Have a View that Sorts by
Subject.  Select all the entries for your document, and Copy (Ctrl+c).  When
you paste into Excel, the pasted table will include the Heading Row.  (ie
Subject, Start, Duration...etc)
Again, not ideal, but maybe a workaround.