Longest jam

I Found a Star on the Ground from the Strobo Trip EP is six hours long and the main reason I feel The Flaming Lips belongs on PA. It's actually rerally great:

-and here's the first twelve hours of the twenty four hour long 7 Skies H3 - but I've only listened to snippets myself:

Having been formed in 1968, the eight-piece Danish band Dr. Dopo Jam had a distinctively late 1960s psychedelic hippy vibe. There are meanderings through jazz-rock synthesis since they also had extended jam sessions that were accentuated by the progressive rock dress of the era. This is an enthralling 25-minute "Opening HELLO" suite from their first record, "Entree," released in 1973. They were able to skillfully incorporate multiple styles into their jam.

Düde Dürst was a drummer from Krokodil, an ensemble of krautrockers from Switzerland. His solo album (1971) has two side-long, lengthy instrumental tracks with a variety of moods and hues and a krautrock vibe that comes from lovely kosmische jamming. This features a lot of elements and amazing percussion pieces that are truly progressive. 

"Chemical Harvest" is a magnificent improvisation that begins with soulful and psychedelic jazz notes and then descends into a mysterious darkness with unusual instrumentation and atmospheres reminiscent of mantras. The song's structure is mostly based on an extensive drum set. The atmosphere is cinematic, eerie, and ritualistic. A bright, cheerful jazz-rocky instrumental featuring dancing flutes and sweeping piano melodies closes the performance. This 20-minute-long track is the quintessential early 70s krautrock and a no-brainer recommendation for lovers of unorthodox, freely improvised jam.