It depends pretty heavily on the specifics of the cosmology, overall.
For instance, take some hypothetical setting where altering the past of a timeline's past simply causes it to be rewritten, instead of giving birth to another timeline. If, somehow, all of these states of the timeline (Both the timeline before it was rewritten and the timeline after it was rewritten) are recorded within some other flow of time (Just like the normal time-axis records a static "picture" of the universe in each of its points), and thus able to be travelled through in spite of the aforementioned alterations obviously being retroactive, then, it is sensible to assume a second temporal dimension is at play here, yeah.
Now, this is where an important distinction is made here: Namely, whether this temporal dimension is continuous or discrete.
A discrete set, as the name implies, is basically one where each of its elements come in steps and are separated from one another by some gap. You can picture that by taking a pen and drawing a few spaced dots on a piece of paper (Pretty much like this: · · · · · ·...), and an actual example of a set like that would be the set of all natural numbers (1, 2, 3, 4, 5...)
A continuous set, on the other hand, is one where there are no gaps between any of its elements, which you can picture by just drawing a line on a piece of paper instead of a bunch of points. An example of that would be the real numbers (Which you obviously can't enumerate, since there's always infinitely-many real numbers between any two numbers you decide to pick, and hence, no gaps between them)
For obvious reasons, if something is explicitly stated to be a timeline or a spacetime continuum, the latter is what we stick to, and in fact, space and time being a continuous set is pretty much the default assumption in physics, and thus, if something is explicitly stated to be a flow of time, it's safe to assume it abides by the latter option.
This is a key point for Low 2-C in particular: If the flow of time is continuous, then it has uncountably infinite points, and therefore, contains uncountably-many copies of the 3-D universe.
However, if there are no explicit statements affirming the existence of a second temporal axis, and instead just an implication that something like one must exist, then it being discrete becomes a possibility. For example, take any verse where a timeline is only created once someone time travels; in such a case, the second temporal dimension would only advance in discrete steps, and thus, it wouldn't really amount to much, tiering-wise.
So, yeah, arguing for that without explicit statements is pretty hard