In this paper we provide general estimates for the errors between the distr
ibution of the first, and more generally, the K-th return time (suitably re
scaled) and the Poisson law for measurable dynamical systems. In the case t
hat the system exhibits strong mixing properties, these bounds are explicit
ly expressed in terms of the speed of mixing. Using these approximations, t
he Poisson law is finally proved to hold for a large class of non hyperboli
c systems on the interval.