  We analyze equilibration times of subsystems of a larger system under a
random total Hamiltonian, in which the basis of the Hamiltonian is drawn from
the Haar measure. We obtain that the time of equilibration is of the order of
the inverse of the arithmetic average of the Bohr frequencies. To compute the
average over a random basis, we compute the inverse of a matrix of overlaps of
operators which permute four systems. We first obtain results on such a matrix
for a representation of an arbitrary finite group and then apply it to the
particular representation of the permutation group under consideration.
