At the interface between engineering, economics, social sciences and humanities, industrial engineering aims to provide answers to various sectors of business problems. One of these problems is the adjustment between the workload needed by the work to be realized and the availability of the company resources. The objective of this work is to help to find a methodology for the allocation of flexible human resources in industrial activities planning and scheduling. This model takes into account two levers of flexibility, one related to the working time modulation, and the other to the varieties of tasks that can be performed by a given resource (multi-skilled actor). On one hand, multi-skilled actors will help to guide the various choices of the allocation in order to appreciate the impact of these choices on the tasks durations. On the other hand, the working time modulation, that allows actors to have a work planning varying according to the workload which the company has to face.