Longest jam

The Ozric's might have had some good jams, but they all died down after John left ... and all of a sudden you had a bass player not as good, a keyboard player having issues with the electronics, and a bit later another new bass player, and another keyboard player, seemingly only playing the saved pieces until another year or two and the kid could do things on his own ... though I still think he is too manipulated and not quite allowed to define his own moments, as it might throw dad off! (Different generation!!!) ... but at least mom is back in ... though I still think that Ed needs to loosen up and let everyone else play a little to help develop better/different stuff. The latest album is good, but not great compared to the stuff of before way back when we got into it! I have not, exactly heard any "jams" by the Ozric's and with the family line up I am not sure we will hear any, though Brandi is playing better, but still too set on what pappa does, and not challenging him. She has the music training, but somehow, I am not sure it translated well to rock music, and jams, and improvisations are not a Berkley graduate forte at all ... 

'Dark Star' 'the other one' and 'Playing in the band' were often stretched to ridiculous lengths!

In the UK, probably Man were the main purveyors of lengthy jams in the 70's often built around riffs from 'Spunk rock', 'C'mon, 'Jam up Jelly tight' and 'Many are called but few get up'.

The Ozric Tentacles (particularly in the early days) used to improv and jam for f***in' hours (man)

Mountain Jam by the Allmans.. good call 

It wasn't rare that music resonated for 6 hours when the Airplane crew held an evening.

Came here to comment this, according to Google, their longest jam is 'Runaway Jim' which clocks in at just under an hour