This idea is inspired by the Hugo-nominated 2004 science fiction novel by Iain M. Banks: The Algebraist. The novel has plenty of interesting ideas but one of the topics that captured my attention is the concept of Slow Seer, people that communicate with some slow-moving aliens. To do that, they live inside special machines that slow down their metabolism enough to match the aliens' pace. It is a lonely pursuit, as the human world around them changes very quickly while they are on assignment.
As far as we know, there are no other animal intelligence comparable to humans in this planet. But it might be the case that we co-exist with more intelligent life (either as an individual or as swarms exhibiting collective intelligence) but we fail to realize because of a difference in time scales. If we could understand, for example, trees within their full life span, we might be able to realize they could be intelligent.
This idea therefore refers to devising tests for intelligence for beings working on a different time scale (similar to the current tests we use on non-human animals, e.g., do they use tools, can they count, etc). With the tests in hand, we can see whether there is historical data to apply to them or if we can start doing them to test by future generations.