In this paper a general fourth-order ordinary differential equation is derived for a class of functions including the time-domain Green function of linearized free-surface hydrodynamics and all its spatial derivatives. Among all the applications following from this new result, the acceleration of numerical computations in BEM solutions of time-domain hydrodynamics was the initial motivation of this work. Two new alternative methods for the computation of convolution integrals based on the new ODEs are suggested and illustrated by a numerical example.