Polymer networks are viscoelastic materials that show both temperature and rate dependent thermo-mechanical behavior. The ability to capture both dependencies using atomistic molecular dynamics (MD) simulations is evidence that the molecular mechanisms underlying viscoelasticity are properly captured by the model. However, direct comparison of atomistic simulations with experiment is challenging due to the large mismatch between the accessible length- and time-scales. Here, we show the utility of the time-temperature superposition principle as a means to overcome this mismatch enabling direct quantitative comparison between simulation and experiment. We study an atomistic model of cross-linked epoxy cooled from the rubbery to the glassy state at five cooling-rates. We show that the use of multiple cooling rates enables objective identification of the rubbery, glassy, and transition region, and calculation of the glass transition temperature (Tg). Further, we study the mean squared displacement (MSD) of the atoms in the matrix at temperatures across the glass transition and find that these trends can be superposed to form a master curve. Using the dependence of the Tg on the cooling rate and the shift factors to form the MSD master curve, we find excellent agreement with experimental data.