Mechanisms of spin/charge interconversion like the spin Hall effect can be used to generate and detect spin currents at timescales ranging from dc to subpicosecond. In the dc regime, the best candidates are Rashba interfaces showing the inverse Edelstein effect, with LaAlO3/SrTiO3 presenting a record conversion efficiency. At picosecond timescales, devices relying on inverse spin Hall effect are efficient THz emitters, but this is less clear for Rashba-Edelstein systems. Here we study the conversion of angular momentum into charge at different timescales in the LaAlO3/SrTiO3 interface. We show that while the effect is exceptionally large in the dc regime, it is reduced by more than four orders of magnitude at the picosecond timescale. This loss of efficiency is discussed in terms of specificities linked to the Rashba state at the interface between these two large band-gap insulators. This has strong implications for the spintronic THz emitters and our work underlines the salient features required for their optimal operation.