I think that's what they do, they just record and edit the output so that they can release it. You're just getting a snapshot.
Oh right. Well I think they have misapplied Eno's idea - since if anybody ever played the 8 hours twice, they'd be repeating it and you would no longer be experiencing generative music.
And in fact it's not even generative in the first place, at least for the listener/consumer. It's generated, but not in front of the listener's ears.
One of the Eno ideas is that each consumer / owner of the app gets their own unique rendition, but only as a one-time listening experience. And then they get another one, and another one - each unique, each ephemeral.
He's all about that idea of the author absenting from the process, setting up the system and letting it roll. Whereas Autechre are very much present, inserting themselves right in the middle of it and saying 'these here are the good bits, these are what you will listen to - and in fact this 8 hour set of sounds is all that you will ever be able to listen to"
I should say though, I have zero interest in listening to generative music, I like repeating things - if it's glorious, then you want that gloriousness exactly the same on each iteration. you might
perceive different facets each time you listen, but the gloriousness as such is definitively achieved - it's product not process.
But he could be right, old uncle Bri.... maybe my attitude is just an un-evolved, hopeless retentive and neurotic collector way of thinking, and in the future people will want the Heraclitean (is that the right word?) flux, the river of sound that is never the same river each time you step in it....