Decision support such as feedback has been considered to be crucial for successful work in many important Dynamic Decision Making (DDM) tasks. However, previous research did not consider the effect of feedback frequency on the performance time which, in conjunction with accuracy, is an important measure of the task performance evaluation in DDM. Therefore, in order to accurately evaluate task performance in a DDM, not only the accuracy of performance, but also the time to perform the task should be considered. This paper will examine the effect of feedback frequency on the task performance time in DDM. Drawing from activation theory (Anderson, 2009), we hypothesized that frequent feedback induces cognitive overload, resulting in learning degradation, and thus producing a U-shaped relationship with performance time. In order to test this hypothesis, we have experimented with the DDM simulation where the frequency of feedback was manipulated. The results demonstrate that there is U-shaped relationship between feedback frequency and performance time ( R2= 0.746, p < 0.01). Our findings show that providing excessively frequent feedback to an operator negatively affects performance time.