So I stumbled upon a feature (that’s been around for a long time) for myself today when looking at the properties of a Word document. I saw this little field called Total editing time and it is in the Details tab of the file’s properties dialog.
Another way to view this is to click on the File menu on the ribbon and look under the properties (to the right) to see the Total Editing Time.
Me being me, I wanted to research this some more. I was initially seeing reports dating back to 2006 that the time is calculated by starting the time from when the document is opened and in edit mode.
From testing I’ve determined that the timer starts when you make the first change and is stopped when you save. It starts again at the next change, and so on.