I'm not suggesting static timestamps, but small audio files of the podcast about to enter, and just exited an ad.
The app could then search for the clips in the podcast to get the timestamp.
If there are copyright issues of sharing small clips, you can just save a hash of a clip, which will allow the app to find a match, but is not itself the Intelecual property of the podcaster; The hash cannot be turned back into the audio file. The hash would be smaller than the audio clip anyway, so sharing hashes would be better
Good idea! I bet you could make good ad library by comparing the audio between episodes of the same podcast (to catch the ads read by the host) and between different podcasts (to catch the targeted ads inserted into a lot of podcasts)