Ok, let's summarize:
- It's not a classic botnet
Probably not, unless the botnet is running inside a corporation's network.
- it's not a gpu farm
Why not?
- it looks like something running in laptops/desktops and not servers.
What makes you say that?
- it has the classic pattern of applications in corporate IT
Apparently.
- it works on Saturdays!
Did it continue into Sunday?
That "Saturday" was Friday somewhere.
I bet for abuse of (a lot of) corporate resources... If so, it cannot be a single person... And this is really, really difficult.
What if it was making optimal use of otherwise unused corporate resources?
I know of an FPGA farm that is used about 30 hours for the weekly regression run, but is otherwise mostly idle.