Instances Dwelling Times (IDT) which consists of waiting times and handle times in a workflow model is a key performance analysis goal. In a workflow model the instances which act as customers and the resources which act as servers form a queuing network. Multidimensional Work-Flow net (MWF-net) includes multiple Timing Work-Flow nets (TWF-nets) and the organization and resource information. This paper uses queuing theory and MWF-net to discuss mean value and Probability Distribution Density Function (PDDF) of IDT. An example is used to show that the proposed method can be effectively utilized in performance analysis of business workflows models which are frequently called by workflow engine.