An explanation is proposed for the time dependence of the neutron emission transient observed after interrupting the electrolysis in Fleischmann-Pons-type experiments with titanium cathodes. It is suggested that the time structure of the neutron emission is related to a reduction of active volume (i.e., the volume with a loading ratio higher than the critical value necessary for cold fusion to take place) in the deuterated titanium. This reduction occurs during the postelectrolysis time due to deuterium transport from the TiDx delta-phase layer to the undeuterated bulk of the cathode. Calculations of the active volume decrease are done by using the Wagner model.