A boundary-element scheme for analyzing initial boundary-value problems of 3-D porelasticity is considered. The scheme is based on a time-step method of numerically inverting Laplace transform. According to the method, a solution in time is calculated using quadrature formulas, based on complex values of the function in specific points. The choice of the points is determined by Lobatto method being one of Runge-Kutta methods. A possibility of using two- and three-stage Lobatto methods is considered. Using as an example the problem about a force, acting upon end of a prismatic poroelastic body, the effect of timestep on the dynamic responses of the forces is studied. The present results are compared with the results obtained on the nodes of Radau method.