There's a webservice which can be used to get a list of content within a specific folder: it is showContents. By setting the parameter "orderBy" to "lastUpdate_D" (where "D" stands for "descending"), you will get the list of content within the folder, ordered by last update. Please be aware that this web service is built to offer a fast and cached instrument for web integrations, but in case of a huge amount of content to be retrieved, an export request is preferable; more information can be found in this article.