Visualization of the definition of infall time. We show the cluster-centric distance of an example galaxy from TNG50 (SUBFIND ID 96768, orange curve) and the virial radius, r_200c, of its host halo (blue curve) as a function of the lookback time in gigayears. The vertical dashed line marks when the galaxy crosses the virial radius of the host cluster for the first time, which we define as its infall time, t_infall.