  The Wigner time delay of slow particles in the process of their elastic
scattering by complex targets formed by several zero-range potentials is
investigated. It is shown that at asymptotically large distances from the
target, the Huygens-Fresnel interference pattern formed by spherical waves
emitted by each of the potentials is transformed into a system of spherical
waves generated by the geometric center of the target. These functions
determine flows of particles in and out through the surface of the sphere
surrounding the target. The energy derivatives of phase shifts of these
functions are the partial Wigner time delay. General formulas that connect the
s-phase shifts of particle scattering by each of the zero-range potentials with
the phases of particle scattering by the potential cluster forming the target
are obtained. Model targets consisting of two-, three- and 4-centers are
considered. It is assumed that these targets are built from identical
delta-potentials with equal distances between their centers. The partial Wigner
time delay of slow particles by considered targets are obtained. We apply the
derived general formulas to consideration of electron scattering by atomic
clusters that trap electron near the target, and by calculating the times delay
of mesons scattered by few-nucleons systems.
