Many models are attempting to describe the fusion process that should lead to the synthesis of super-heavy elements (SHE) in order to help the experimental quest. But there are still too many uncertainties on some key parameters to do reliable predictions. The few evaporation cross sections available are not enough to validate the models and one has to find other means. In this seminar, I will present some criteria that should help to characterize the barriers that should be or not be crossed to form a SHE. Some experiments were performed at GANIL to try to locate the island of stability of the SHE by measuring the fission time. Based on the crystal blocking technique, they have shown some direct evidences for very long fission times of the SHE. Is this observation due to a high fission barrier or to other mechanisms? I will present some fission-time calculation made with KEWPIE2, which is a new dynamical cascade code devoted to the SHE. It has been first compared to the evaporation cross section obtained by cold and hot fusion in order to fix the only two free parameters. The calculated fission time distribution will be analyzed and compared to the experimental results in order to get some constraints on the fission barrier. The saddle-to-scission time cannot be neglected for these nuclei. For that purpose, we derived a new formula that can accommodate any kind of potential. I will show some preliminary results on the influence of isomeric potential pockets. As for the fusion part, the fusion hindrance that is commonly explained by the existence of a second barrier on the way to the ground state gives some constraints on the neck parameter. I will show our latest results on the subject.