Underestimating the duration of the production process is one of the basic factors determining the occurrence of delays in the duration of individual operations included in the production process. Occurrence of underestimation of production time brings many negative effects, which include, among others: underestimation of the company’s production capacity, accumulation of intermediate stocks, impeded planning of the production process (scheduling of the production process) and increase of production costs. The problem of erroneous estimation of the duration of the production process is most often found in production plants specializing in serial or mass production, implemented in a parallel or series-parallel system. The basic causes that underestimate the duration of the production process include errors in production scheduling, incorrect determination of durations of individual operations carried out as part of the analyzed production process, complexity of production operations and employment structure. The occurrence of delays in the production process can also be affected by accident events that generate underestimation and costs for the enterprise (including social and economic costs). In many cases, many algorithms are used to reduce underestimation and optimization and scheduling of the entire production process. The publication presents an analysis of the production process in which the duration of the production process is underestimated, taking into account the employment structure in the manufacturing company. The analyzes allow to determine the level of underestimation of operations of the production process depending on the form of employment (steel workers – employed under a contract of employment in the production plant, and temporary workers employed by temporary work agencies), identification of the reasons for the underestimation of individual production positions and the length of their time occurrence.