Rated 5 out of 5 stars

I really like this extension, and had been looking for it for a while.
There are still some problems with the timestamp, but I fear it depends on Windows 7 rather than on your extension. Sometimes, not always, you have problems with the timestamp in these cases: 1) if you add a prefix - by chosing the "add a refix" feature - to the filename of the file to be exported; 2) if you export new messages to a folder in which there are already exported EML files: it may happen, but does not always happen, that th previously exported files change their timestamp to the current day and time (as it happens with Windows 7 when you copy/move an EML file)

This review is for a previous version of the add-on ( 

maybe it's already there?

I don't know if I've understood your question (I've not win7), but maybe the feature you ask is already there: go in extension options panel and enable "Add date to file properties" (yes, the label is too cryptic!!!). Did you mean this?