Q: What tier is transcending space and time?
A: As said above, "transcending space and time" is a very vague statement by itself and can mean multiple things depending on the context in which it is made, as well as how this characteristic is portrayed in the first place. It is perfectly possible for such a statement to mean that a character is simply "untied" from the universe's spacetime, and is thus unaffected by alterations in the timeline and similar meddlings. Likewise, it's not exactly uncommon for time travel (Or any action / process that affects something through different points in time) to be described as "transcending time and space."
However, if it is specified that they "transcend space and time" in the sense that they exist on some higher level of reality that is outright superior to a spacetime continuum in nature, then they should be put at Low 1-C, assuming the continuum in question is one comprised of four dimensions. The answer may vary depending on this factor.