You probably want to do this:
Note the start value "-2" which indicates that the source of the scheduled stream is a live stream.
<playlist name="pl1" playOnStream="Stream1" repeat="true" scheduled="2013-04-22 10:00:00">
<video src="testDVR.stream start="-2" length="-1"/>
Then you have to start testDVR.stream in the Manager by adding to StartupStreams, or using StreamManager.
You can then play "Stream1", which in this configuration is just wrapping testDVR.stream. The scheduler is not doing anything in this case, but you can mix file sources, and other live streams in endless configurations.