The paper focusses on the derivation of the time-homogenized constitutive equations of the high-temperature steel X20CrMoV12-1 which is mostly used in power plant components. For this purpose, the two-time-scale approach is briefly introduced first explaining the homogenization procedure. The constitutive model considered is described including evolution equations for the inelastic strain and the two inner state variables the backstress and the softening. In the main part, the application of the two-time-scale method to those equations is shown also taking the numerical implementation into account. Since the material is subjected to high mechanical and also thermal loadings leading to highly non-linear behavior, a cyclic test is simulated in the end.