I wonder if this simple analogy can help. Suppose we have a pool of water and drop a stone into the middle. The waves move out with initially small wavelength. As they travel, the wavelength will increase. Someone measuring the time between wave crests will see a 'dilation' effect. Mathematically, is there a difference between this stretching and the spacetime stretching of the BBT? In the paper by Blondin et al. in the OP, Appendix A gives the time dilation derivation for the latter. I'm thinking I can work these equations for the effect I'm describing. I emphasize that this is just an analogy. I have a more detailed model for what's happening, which I linked to above.