Among imperfect maintenance models, hybrid ones give interesting results when modeling the effect of replacing one or several components on the behavior of a multi-component systems, whatever their configurations. The herein paper, which concerns series systems, aims at studying the effect of the replacement time and the number of replaced components on the imperfect maintenance hybrid model with three parameters (i.e. geometric and arithmetic adjustment of failure rate parameters and virtual age adjustment parameter). A mathematical model is then fitted for each hybrid model parameter. This will allow a realistic modeling and planning of maintenance tasks of series systems.