I baked a whole scene at 4096px and 4000 samples, took 14 hours, longest for me. can you beat that? 
and what was your settings and verts count?
Action:
UV Texture bake full scene
Settings:
4096px
4000 samples
18hrs
I once read about a 709 hours render in Terragen 2 :D.
Yikes, how big was the scene?
Three weeks. Not kidding. This was in the early 90’s iirc, and not Blender. Pure raytracing. And I messed up the settings, so when it was all done I couldn’t believe I had forgot to turn on shadow casting (or something equally critical) for an important object in the scene.
Omg. Even found it 
Apparently 1994, as it has that info engraved in on of the objects. Size, a whopping 768x576 - super high res at the time, lol
I read that the 3 citywide render farms for Big Hero 6 could render Tangled from start to finish in about 10 days.
so 240 hours?
I’ve calculated how much time it would take to render Big Hero 6 only on 4 core processor. (Their renderfarm had 55’000 cores)
And it was something around 7000… years.