This answers the original, unedited question:
What is a good paper—using COBE, WMAP, or Planck data—that shows that the CMB anisotropies do or do not vary on timescales much shorter than cosmological timescales (say, the Hubble time)?
I am letting it stand because now above is another question.
In cosmology, a Hubble volume, or Hubble sphere, is a spherical region of the Universe surrounding an observer beyond which objects recede from that observer at a rate greater than the speed of light due to the expansion of the Universe.1
The comoving radius of a Hubble sphere (known as the Hubble radius or the Hubble length) is c/H_0, where c is the speed of light and H_0 is the Hubble constant. The surface of a Hubble sphere is called the microphysical horizon,2 the Hubble surface, or the Hubble limit.
In this review paper it is the Hubble radius ( actually Hubble time multiplied by c ) that controls whether anisotropy will appear in CMB.
On scales large compared to the Hubble radius at last scattering, only gravity
is important but on smaller scales the acoustic physics of the primordial plasma and
photon diffusion dominate.
So there is a different behavior of the regions of the universe as it is expanding and it is reviewed in the paper.