Let's not forget that intros/outros are usually really low bitrate, as the images are usually really simple (a lot of text on a dark background). So you might save about 5% of run-time, but that could only equate to 1% of the file size.
Comments on Options for deduplicating storage of TV series intros
There's no guarantee that either the intro nor outro has low bitrate. I would expect this to be as different from program to program as any other part of the program. For example, many anime programs has swooshy-rappidly switching scenes as their intros.