Hey tkim. I saw your post @UnknownTimezoneError / pytz quirks, and it helped tremendously.
I am not able to use modified because that gets timestamped even when a non-substantive field such as table_of_contents gets changed. I wanted to originally write the add-on to only check when items are changed in the default fieldset, but that got a little too unpredictable. So I opted to only track edits by members of certain groups so that if an administrator updates a link, it doesn't show that as the last modified. Currency of our information is important. Therefore knowing the date the page was actually reviewed by a SME as opposed to an administrator is important.