When you start to upload a file in the RadUpload control, the control has a reference to the FileInfo object describing the file. You can access it in the FileUploadStarting event handler through the e.SelectedFile.File property. However, you can get the CreationTime property of the FileInfo object only in a trusted application. Here you can find more information about the FileInfo class and its properties.
This basically means that in a trusted applicaiton you can get the CreationTime of the file that is going to be uploaded and save it somewhere on your client-side or pass it to the server side as described here.
All the best,
the Telerik team