  The concepts of Wigner time delay and Wigner-Smith matrix allow to
characterize temporal aspects of a quantum scattering process. The article
reviews the statistical properties of the Wigner time delay for disordered
systems; the case of disorder in 1D with a chiral symmetry is discussed and the
relation with exponential functionals of the Brownian motion underlined.
Another approach for the analysis of time delay statistics is the random matrix
approach, from which we review few results. As a pratical illustration, we
briefly outline a theory of nonlinear transport and AC transport developed by
B\"uttiker and coworkers, where the concept of Wigner-Smith time delay matrix
is a central piece allowing to describe screening properties in
out-of-equilibrium coherent conductors.
