The influence of the duration of the stimulating laser pulse in the photodesorption of NO from a NiO(100)-surface is studied theoretically within a two-dimensional quantum wave packet approach. The complete event including laser-induced excitation and subsequent electronic relaxation is treated consistently from first principles within the surrogate Hamiltonian approach for open quantum systems. We demonstrate that the common assumption of time-scale separation of excitation and relaxation does not hold if ultrashort femtosecond laser pulses are used. We predict a significant effect on rotational distributions of desorbing molecules if the time scales of electronic excitation and relaxation are similar. (c) 2006 Elsevier B.V. All rights reserved.