On the way to collectivity in rarely interacting systems

<!--HTML-->We present the time resolved evolutions of the anisotropic flow coefficient $v_n$ with consideration of both the linear and non-linear dependence on the initial eccentricities $\epsilon_m$. The relativistic Boltzmann equation is utilized in the few collision regime in order to model the evolution of the phase space distribution. Our analytically calculated time-dependent flow harmonics are compared to results of transport simulations. Eventually, we discuss the important impact of the non-linear eccentricity contributions on the dynamical build-up of flow coefficient.