Step 13 : Since the time to exit is the same for all packers ,let's specify the travel from the packers to the exit using a " Model Property " via the " Definitions " tab . Insert a Expression property from the "Standard Property" drop-down named TimeToExit and give it a Default Value of 3.5 with Unit Type pf Time with Default Units as Minutes . Since this an " Expression" property then on could specify a expression for the time to exit (e.g., Random.Part (2,3.5,7). If it was numeric property then only constant values could be used(i.e., 3.5)