The characteristic time scaling of the electron flux evolution at geosynchronous orbit (GEO), resulting from the quasilinear wave-particle interaction, is investigated. The upper limit of the electron flux increase rate, due to the interaction with waves, is deduced from the energy diffusion equation (EDE). Such a time scaling allows for a comparison with experimentally measured fluxes of energetic electrons at GEO. It is shown that the analytically deduced time scaling is too slow to explain the observed increase in fluxes. It is concluded that radial diffusion plays the most significant role in the build up of the energetic electrons population at GEO. However, this conclusion is only justified if the seed population energies are very low.