The dynamics of predissociating high molecular Rydberg states of NO below the lowest ionization threshold is computed in the presence of a weak external dc field using a quantum theory based on an effective Hamiltonian formalism. The core-electron interaction affecting the low l states (l less than or equal to 2) is taken into account by molecular quantum defect theory, while for the high l states (l greater than or equal to 2), a long range multipolar expansion is used to describe the effect of the anisotropy of the molecular core. Time- and frequency-resolved ZEKE spectra are computed. In the energy range investigated, the decay kinetics of the ZEKE intensity is found to exhibit two time scales, which differ by more than an order of magnitude. The short decay constant typically falls in the submicrosecond range and is in agreement with previous experimental results and computations. In addition, our computations predict a long-time component, which decays in the tens of microseconds range. The two decay times are discussed in terms of the short and long range interseries dynamics, in terms of the strength of the external dc field, and in terms of the nature of the bottlenecks in phase space for a predissociating molecular core with a rather large rotational constant (BNO+ = 1.9842 cm(-1)). It is found that for this particular case where all series are coupled to the fragmentation channels through a low l bottleneck, the predissociation process does not quench the long time component in the decay kinetics. The reason is that the interplay between the interseries coupling and the external dc field leads to a shift of the decay constants to larger values together with an enhancement of the weight of the long time component in the decay kinetics. Special attention is devoted to the role of the dipolar interaction and its synergy with the external dc field.