  We re-consider the time dependent Schr\"odinger-Newton equation as a model
for the self-gravitational interaction of a quantum system. We numerically
locate the onset of gravitationally induced inhibitions of dispersion of
Gaussian wave packets and find them to occur at mass values more than 6 orders
of magnitude higher than reported by Salzman and Carlip (2006, 2008), namely at
about $10^{10}\,\mathrm{u}$. This fits much better to simple analytical
estimates but unfortunately also questions the experimental realisability of
the proposed laboratory test of quantum gravity in the foreseeable future, not
just because of large masses, but also because of the need to provide
sufficiently long coherence times.
