  We derive the necessary conditions for implementing a regulator that depends
on both momentum and frequency in the nonperturbative renormalization group
flow equations of out-of-equilibrium statistical systems. We consider model A
as a benchmark and compute its dynamical critical exponent $z$. This allows us
to show that frequency regulators compatible with causality and the
fluctuation-dissipation theorem can be devised. We show that when the Principle
of Minimal Sensitivity (PMS) is employed to optimize the critical exponents
$\eta$, $\nu$ and $z$, the use of frequency regulators becomes necessary to
make the PMS a self-consistent criterion.
