[en] The effect of finite temperature T and observation time t on the microwave absorption in ferromagnetic resonance (FMR) has been investigated in the framework of a Preisach model for planar aligned single particle volume systems. The Preisach-Neel model is used to select the particles which are blocked or in a superparamagnetic state from a system and to compute the susceptibility of the system from the individual particle susceptibility. By making the observation time constant, we express the FMR susceptibility as a function of temperature. An increase of the resonant frequency and a decrease of FMR resonance width with the temperature increase were observed