UX is an app to assist user experience designers time how long it takes users to complete tasks during usability tests. Create tests for each app your are testing and then create and customize the tasks you will have the user go through in your product. When you start the test you will be able to time how long the user takes to complete each task.
At the end of the test you can click "capture" to take a screen shot of the times it took that user to conduct each task. These screenshots are stored in the UX photo album of your iPhone.