The process of formation of the participant system in heavy-ion collisions is investigated in the framework of a simplified analytic Glauber-like model, which is based on the relativistic Boltzmann transport equation. The key point lies in the time-dependent partition of the nucleon system into two groups: nucleons, which did not take part in any interaction before a given time, and nucleons, which already have interacted. In the framework of the proposed model we introduce a natural energy-dependent temporal scale tc, which allows us to remove all dependencies of the model on the collision energy except for the energy dependence of the nucleon-nucleon cross section. By investigating the time dependence of the total number of participants we conclude that the formation process of the participant system becomes complete at t≃1.5tc. Time dependencies of participant total angular momentum and vorticity are also considered and used to describe the emergence of rotation in the reaction plane.