Probably we all would like to know the execution time in advance. However, as Dwaine pointed out, so many variables have an influence on this, and therefore an a-priori estimation is difficult. From my point of view, only the modeler himself can give a rough estimation based on his knowledge of the model properties and ways of setup. But this of course requires long-term experience with the kind of model to be built. It is nearly impossible to estimate simulation times externally based on a small amount of information.