In this talk I will describe how we can get information about the thermalization time of the QGP by using dileptons. I discuss the calculation of dilepton production from an anisotropic quark-gluon plasma by using a space-time model for the non-equilibrium phase of the QGP. The model interpolates from early time expansion (tau << tau_iso) to ideal hydrodynamic behavior at late times (tau >> tau_iso). I show that high-energy dilepton production is sensitive to the assumed plasma isotropization time, tau_iso, and can therefore be used to experimentally determine the time of onset for hydrodynamic expansion of a quark-gluon plasma and the magnitude of expected early-time momentum-space anisotropies. Finally, I will briefly present a method to describe the 0+1 expansion dynamics at very early-times of the firewall in ultrarelativistic heavy ion collisions.