Regarding the "Song length detect limit" wrt Icecast, would it be possible instead for Centova Cast to use the duration of the source MP3 file rather than subtracting timestamps? It seems like this would solve the problem, obviate that setting, and result in more accurate statistics.

I assume you're someone who never broadcasts live.  Arguably the majority of stations will at *some* point do the occasional live broadcast, which is the main reason this approach is unsuitable.

The other major problem is that your MP3s would all need to be CBR-encoded.  If they're VBR-encoded, the only way to accurately determine their length is to analyze the *entire* MP3 which is prohibitively slow to do in PHP.  That's not so big a problem in the upcoming v3.0 release of Centova Cast, whose backend is written in C, but for the current pure-PHP release it's not suitable.