I'd rather see a jam chart with the "Highly recommended" versions of songs regardless of length. Some people get too excited about length of jams, especially the 20minute mark for some reason. It is no indication of quality in my opinion. I'll always take 14 minutes of unique and focused jamming over 24 minutes of noodling around.
I understand that a longer track time gets people excited about what the jam might contain, but why has the jam band community decided 20 minutes is significant? Not trying to pick on you OP, it just seems so arbitrary to me...