The construction of timing models to describe the functioning of production systems is considered, along with their application in the reengineering of systems in ferrous metallurgy. Timing models are classified in terms of their purpose, the scale of the system being described, the degree of continuity of the material flux, the quantity of intermediate products processed at once, the number of production operations, the importance of the equipment, the statistical timing characteristics, the degree of mechanization and automation of the equipment, and the material inputs and outputs. The productivity is shown to play an important role. Its relationship with other characteristics of the production system is established. A factorial model is proposed for the productivity of the system. The fundamental factor is identified: the time step. The basic formula for estimating the productivity on the basis of the time step is derived. A method is outlined for analysis of the bottlenecks in the production system on the basis of a timing approach and estimation of the efficiency of reengineering measures. As an example, the timing model is used to find the bottlenecks in rolling systems. Timing models may be used in the planning, prediction, and real-time control of production.