In Greg Egan's diaspora, they touch on things like this. I can't remember specifically but at one point they encounter a planet where there is some process tha

In Greg Egan's diaspora, they touch on things like this. I can't remember specifically but at one point they encounter a planet where there is some process that is turning complete, and they realize an entire universe is simulated in the process with sentient beings that they can never communicate with. I can't remember the details so I'm butchering it a little, but it's a great read. Diaspora and Permutation City also touch on the topic of speeding up or slowing down conscious so that millenia pass in subjective seconds, or a subjective second passes in a millisecond, etc.