In Windows 8, the best you can do where background tasks are concerned is a Timer trigger, but that gives you only a resolution of 15 minutes. It's a known deficiency for this scenario.
Fortunately, it's addressed in Windows 8.1, where the BackgroundTransfer API lets you configure a toast notification to be displayed when the transfer is complete. See the BackgroundUploader.SuccessToastNotification and FailureToastNotification properties.
I talk more about this in Chapter 4 of the second edition preview of my free ebook.