The interaction of light with Cholesteric Liquid Crystals (CLC) in the presence of rime dispersion, magnetooptical activity and absorption is considered. The magnetooptical activity leads to the waves irreversibility, i.e. to the absence of center of symmetry for the surface of wave vectors and other surfaces, characterizing the direction dependence of optical properties (the nonequivalency of the forward and backward directions of propagation occurs). The waves irreversibility effects in CLC and their influence on the geometry of the Bragg reflection are considered. The time dispersion leads both to the splitting of region of diffraction reflection, and to the appearance of new region of diffraction reflection. Near the isotropic point it is possible to get a narrow region of diffraction reflection with tunable width and location. The results present also interest for the electrodynamics of media with waves irreversibility. They can be used no only in CLC optics but also in microwave electrodynamics of artificial ferromagnetic helical media.