The time characteristics of a flow of large rare gas atomic clusters formed by supersonic expansion of a gas into vacuum through conic nozzles are studied using the time resolving Rayleigh scattering method. The results show a two-region structure of the time resolved spectrum of the scattered light from the clusters. The average cluster size in the second region is much, even orders of magnitude, larger than that in the first one. Three designs of the valve-nozzle assembly have been used to investigate the origin of this finding. Finally, the potential application of the observation is proposed.