Single server queueing system with two Poisson input flows of rate λ1 and λ2, finite queue of size R - 1 < ∞ and bi-level hysteretic policy is considered. Customers of λ1 flow are served with relative priority. Customers of both flows are served with the same constant service time. Bi-level hysteretic policy implies that system may be in three states (normal, overload, blocking), depending on the total number of customers present in it. New method for calculation of mean return time to normal operation state is proposed. © 2013 Springer-Verlag.