I don't listen to long music as much as I probably should because I'm a very impatient person.
That said, when I do end up listening to the longer ones they immerse me much more than shorter songs into a certain mood.
I don't really just sit there and listen to short songs, they accompany my doing other things.
Longer songs will sink me into them though, it's a really nice feeling.
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I love long songs too. They're kind of trance inducing.
As for recommendations:
The Doors- The End
The Velvet Underground- Sister Ray (also check out the live version, it's even longer)
1983… (A Merman I Should Turn to Be)
Abbey Road side 2
The Kilimanjaro Jazz Ensemble- Lead Squid
Anything by Myrrors if you like psych rock
Wooden Wand & the World War IV- Our Father the Monster (highly recommended)
Also not sure if it's your thing, but I really enjoy long international music. Sitar pieces by Ravi Shankar, Djivan Gasparyan (Pangea is a good mixed album), Naseer Shamma (Hadatha fi al 'Amiriyya is great) etc.
That's all I can think of off the top of my head.