Neutron diagnostics offer one of the most direct ways to obtain information about the deuteron characteristics in fusion plasmas such as densities and temperatures. Thus, neutron diagnostics are of increasing importance for future fusion devices and efforts are being made to improve the present methods for interpreting neutron signals. Until now, however, the derivation of deuteron densities as functions of time for non-stationary neutral beam heated plasmas, i.e. where the velocity distribution of the plasma deuterons is highly non-Maxwellian and steady-state conditions have not been reached, was only possible in very few cases with the aid of slow, complex codes. Here, we present a comparatively fast, time-dependent code for neutron rate interpretation of neutral beam heated tokamak plasmas which is based on a Fokker-Planck model for injected ions. The code includes tail-tail fusion reaction rates, which are important but often had to be neglected since they are difficult to calculate. Results from the code are presented for test cases in order to illustrate the time-scales involved in neutron production. Finally, time-dependent inter-pretation calculations for JET hot-ion mode discharges are presented, and the results for the inferred dilution nD/ne are shown to be in very good agreement with the experimental data.