Apparently not. This information is stored in the database and not user accessible (unless you use a database manager to open the catalogue). Lightroom updates this "Edit time" each time you do anything to an image, including change the rating or colour label.
If you want to know when an image was "modified" by changing a paramenter in the development module, the history now shows date and time of the last modification, which is not necessarily the same as the "Edit Time" used in the library module to sort, as the History does not record when you change things like rating and colour labels