Showing Date of Most Recent Contents Modification

It would be good if Windows Explorer could, when it's listing the details of a folder, optionally show the time of the most recent update to the folder's contents. By the most recent update I mean the modification time for the most recently modified file within the folder's (transitive) contents. This way, when I’m backing up folders, I can easily tell whether any changes have been made within a folder since I last backed it up.

Another use for such a detail would be sorting folders based on how recently an update was made to them. I think this would be quite useful, as only a small majority of folders are that actively used, if my experience is anything to go by, and if you equate activity with relevance then such sorting would allow you to more easily focus on these relevant folders and ignore the less relevant ones.