  The propagation of the excess of quasiparticles and phonons produced by a
nuclear recoil inside Sn and Zn superheated superconducting granules will be
discussed. The decay towards equilibrium of the initial disturbance is assumed
to be a thermal diffusion process described by a set of coupled heat flow
equations for the effective quasiparticle and phonon temperatures. The solution
is carried out analytically for a point source located anywhere inside the
superconducting granule with the initial energy distributed in both
quasiparticle and phonon systems. The calculated time delay between the neutron
interaction and the nucleation of the phase transition will be compared to the
time delay distributions obtained by irradiating Zn and Sn SSG detectors with a
70Me$\!$V neutron beam.
