  We provide an exact description of out-of-equilibrium fixed points in quantum
impurity systems, that is able to treat time-dependent forcing. Building on
this, we then show that analytical out-of-equilibrium results, that exactly
treat interactions, can be obtained in interacting quantum impurity systems in
their strong coupling regime, provided they are integrable \emph{at}
equilibrium and they are "super Fermi liquids", i.e. they only allow for
integer charge hopping. For such systems we build an out-of-equilibrium strong
coupling expansion, akin to a Sommerfeld expansion in interacting systems. We
apply our approach to the Interacting Resonant Level model, and obtain the
exact expansion around the low energy fixed point of the universal scaling
function for the charge current as a function of voltage, temperature, and
frequency, up to order seven.
