In this talk I will introduce a rather recent scaling method allowing to perform the usual equilibrium finite-size scaling analysis for continuous phase transitions in the out-of-equilibrium relaxation regime. Such an approach is most valuable for all those system which show a very slow critical dynamics – i.e. a high value of the dynamic exponent z – and systems which are computationally expensive to simulate. I will show results obtained for the three-dimensional IsingSpin Glass (z ~ 6.8) relaxed via the Metropolis dissipative dynamics. The values of the critical exponents and critical temperature are the first out-of-equilibrium estimates to be compatible and comparable in precision with those obtained from the "Janus" dedicated supercomputer. Since the method is based on Renormalization Group arguments it turns out to be completely general and, potentially, of wide interest in different domains. Furthermore, I will summarize some results obtained in the development of the numerical implementation of such simulations optimized for GPU architectures. [1] M. Lulli, G. Parisi and A. Pelissetto, PRE 93, 032126 [1](2016), http://dx.doi.org/10.1103/PhysRevE.93.032126 [2] [2] M. Lulli, M. Bernaschi and G. Parisi, CPC 196 (2015) 290–303, http://dx.doi.org/10.1016/j.cpc.2015.06.019 [3]