A phase-space plot is a simple plot of clustocentric velocity versus clustocentric radius of all satellites in a cluster or group. Using numerical simulations, we demonstrate how such a diagram provides valuable information on the infall time of the satellites into their cluster or group. This is a crucial information for better understanding environmental effects, because they do not act instantly and generally take time to have a strong impact on their satellites. In this way, we move beyond simply noting a galaxy's current environment, and add a time dimension as to how long they have been in that environment. We derive a variety of approaches, that can be applied to observed groups of galaxies, to constrain how galaxy properties (such as star formation, gas fraction, morphology, etc) change as a function of time spent in their host.