You will need to make sure that this particular live stream is already published on this particular application. Assuming that your application is called "ucbtv1" and the live stream published to this application is called "myStream", then your streamschedule.smil file would look something like this:
Setting the start="-2" parameter would mark this stream as a live stream. Having this in place, at the scheduled time, the live stream will play back for 300 seconds, and then move to the next playlist item.
This would play back the 3 video files for 10 seconds each, and them switch to the live stream for another 300 seconds. Since the playlist is set to "repeat", after the 300 seconds of live, the playlist will start from the beginning.