This paper presents a study of the real-time control conditions for a robotic system with visual servo control. The system is based on an industrial manipulator with a modified controller allowing real-time joint-level control. The work is particularly concerned with delays and path deviations. The focus is on the Line-of-Sight based path tracking controller. The paper describes an analysis of the different delays in the sensor-robot system and a model is presented based on the overall delay. Further the stability of the modeled system is analyzed in respect to a specific control case. The correctness of the estimated system delay is indicated by comparison of simulated and experimental results.