The recruitment of young PhD graduates in the academic sector is associated with great uncertainty regarding their potential teaching and research productivity. Thus, in order to recruit the best PhD graduates for permanent positions, employers (universities or research institutions in France) select according to signals sent by the applicants in their curriculum vitae: publications, post-doc position, host research institution.... In our paper, we analyse the factors affecting the access duration to a permanent job in three academic fields in France, using a sample of PhDs graduated in 2001. A discrete-time model, controlling for post-doc participation, is used to analyse the main factors influencing access duration. Our main results indicate that postdoc appointments have a positive influence on the access duration to a permanent job in chemistry and life sciences, and to a lesser extent, in mathematics, physics and in the applied sciences, which is coherent with the idea that potential employers use this information as a proxy for research and teaching abilities.