In many cases the timeliness of production is not satisfying. The reasons are multifaceted. In order to minimize the impacts of schedule deviation with respect to the (external or internal) client, there is a necessity to take safety lead times into consideration when scheduling production orders. The resulting high level of work in process goes along with high costs respectively that have to be taken into account when dimensioning the safety lead times. This article presents a decision model describing the dependencies of safety lead times, work in process costs and timeliness of production quantitatively in order to evaluate improvement measures concerning schedule reliability. This cause-effect-model is an essential keystone for illustrating the scheduling dependencies of a supply chain.