The waiting time is crucial for assessing traffic quality at intersections. Non-stationarity, or fluctuations in traffic intensity, is only partially included in the methods for determining waiting time. This study analyzes the occurrence of different types of non-stationary traffic intensity profiles, investigates their impact on waiting time through microscopic traffic flow simulation, and proposes a new factor for better consideration within the methods. Vehicle delay is used to evaluate the service level for intersections. The influence of non-stationary arrival flow rates has only been partially incorporated into calculation methods. Empirical data show that traffic volume during peak hours can be distributed in very different forms. A microscopic traffic simulation study is conducted to assess their impact on delay.