Oh man, I agree that sometimes jam sessions are boring, but I’ve heard many that are not.

You do you, but for me, some jams are just sublime, the longer the better in those cases.

For example -https://youtu.be/kAUs187IT4I

Norman Granz’ Jam Session #2 (1953)
Alto Saxophone – Benny Carter, Charlie Parker, Johnny Hodges
Bass – Ray Brown
Drums – J.C. Heard
Guitar – Barney Kessel
Piano – Oscar Peterson
Tenor Saxophone – Ben Webster, Flip Phillips
Trumpet – Charlie Shavers

Real improv, real gone, man! :)