On the time question, I rountinely podcast 30-60 minutes of programming, followed by 4 or 5 hours of quiet meditation. The silence compresses down to about 5-10 megs. On the mechanical rights question, this is a difficult one, and you should consult an attorney before you walk down this path. One view is that sound files embedded in a longer recording, which cannot be excised easily to make independent recordings, are covered by the statutory license. Another view is that you'll need yet another license, this one from the Harry Fox agency. (http://www.harryfox.com/). Bret