Business Process Modeling Notation (BPMN) is nowadays widely used by companies to represent their business processes. Such processes are usually designed and written by non-expert users for whom the main matter is to conceive a process corresponding to the needs of the companies. As the quality of the process is not the main design criterion, it can generally be optimised in several ways. For instance, reducing the financial cost of the process, its resource usage, or its execution time are classical optimisation axes. In this work, the considered BPMN processes are enriched with time and resources, and are executed multiple times. The proposed optimisation approach consists in reducing the execution time of these processes. To do so, the method presented in this paper consists in restructuring the processes by changing the position of their tasks. The goal of this restructuring is to limit the overuse of the resources and consequently reduce the execution time of the processes. To avoid generating unsuitable processes, the designer is involved in the restructuring phase, as (s)he validates each restructuring step. The proposed technique is fully automated by a tool that was implemented and applied on several examples for validation purposes.