In standard cosmology, there is a general picture of:
- Primordial nucleosynthesis, i.e., when and how, nuclei or elements were formed. It is not quite tested, but it is more or less known where it yielded.
- Decoupling of light (Big Bang, CMB) moment, after giving rise to the first elements.
- Decoupling of gravity at Planck time.
- The moment of inflation.
What do we know about dark matter origins and decoupling from the rest of the fields if is "real" (I give up DM as modified newtonian dynamics or modified gravity at this questions), and how could we test, if any, that decoupling? Related: if dark matter decoupled at some moment, should we expect a dark matter cosmic background, similarly to the CMB or the hypothesized cosmic neutrino and relic graviton backgrounds?
In summary: the question is, do we know when DM formed, if any, at the early Universe from standard cosmology?
Of course, I presume that BSM is necessary in order to do some guesses about dark matter, as this is not quite to look at the peaks of the CMB anisotropies.