It was not oversold. In fact, it sold very little nationally as few national advertisers would go within a mile of it.Plus his show was oversold like crazy leading to 10+ minute stopsets. Even die-hard fans won't sit through that.
The show had local breaks, which were timed to "whenever Stern wanted to go to a break". Sometimes two breaks met together, for over 10 minutes of ads. There was no structure in a formal sense, and Stern would drag subjects out across multiple quarter hours, and lots of people would get to work or their destination and never hear the end of each segment.