  Putting a general, physically relevant upper bound on equilibration times in
closed quantum systems is a recently much pursued endeavor. In PRX, 7, 031027
(2017) Garc\'{\i}a-Pintos et al. suggest such a bound. We point out that the
general assumptions which allow for an actual estimation of this bound are
violated in cases in which Fermi's Golden Rule and related open quantum system
theories apply. To probe the range of applicability of Fermi's Golden Rule for
systems of the type addressed in the above work, we numerically solve the
corresponding Schr\"odinger equation for some finite spin systems comprising up
to 25 spins. These calculations shed light on the breakdown of standard quantum
master equations in the "superweak" coupling limit, which occurs for finite
sized baths.
