But I thought it was good 25 years ago
Actually, I just googled and see they put some out in 2003/2005. I thought it didn't make it past the 80s.
The standard ones were 60/90 minutes (30/45 per side), granted the tracks would have to be broken down so that you have full tracks on each side, but you'd still be able to fit 55+ minutes on a 60 minute cassette.
The standard LPs (records) could do ~25 minutes per side, so that's a bit mire limiting.