I trained it for about 24 hours, although there didn't seem to be that much improvement after the first 12 or so. Generating a song with the trained network actually happens almost in real time. I'm tempted to try to make it continuously generate new music and stream it, but even the small cost for the instance would start to add up, so I haven't actually tried setting that up yet.

Another interesting data point: the learned set of weights ends up being about 15MB.