Dolores Cannon says we are in 5D already

[Infinite]

Given the process is approx 150-700 earth years if my memory serves me, then how in the world can we be transitioning into 5D? Are these folks implying 5th dimension but in the 4th Density? Aren't Density and dimensions the same thing?

There are many, many views on the organization of dimensions in various esoteric, spiritual and new age sources. The idea that we are going to 5D is due to the fact that many believe that time is the fourth dimension. I don't particularly see any sense in that, I see dimension as a concept referring to space. Although technically space and time are one thing, then it doesn’t make any sense to take time as something apart.

About Ra's terminology, they used the terms "density" and "dimension" interchangeable, but also as different concepts. Here Ra speaks of our 5D:

...we have never been gone from your fifth dimension and have been working in this last minor cycle to prepare for harvest

.(14.4)

Ra explains here what density would be:

The term density is a, what you would call, mathematical one. The closest analogy is that of music, whereby after seven notes on your western type of scale, if you will, the eighth note begins a new octave. Within your great octave of existence which we share with you, there are seven octaves or densities. Within each density there are seven sub-densities. Within each sub-density, seven sub-sub-densities, and so on infinitely.

(16.51)

And here they use "plane" and "sub-density" as synonyms:

One more; that is, the permeability of the densities so that there may be communication from density to density and from plane to plane or sub-density to sub-density.

(90.25)

So, for me, sub-density, dimension and plane are the same thing. Thus, density is a vibratory spectrum where there are infinite divisions (the dimensions) that are organized in a power of 7.