[ewilliams]

E. Lammers's response is excellent and generalizable. In the software being used, find the system variable keeping track of the number of times the task has been done (most softwares provide such a system variable) and use it to define the task time as a decreasing function of the number of times the task has been done (this time can be assigned to a modeler-defined variable used as the cycle time (task time). Furthermore, if the time required increases with the number of task completions (modeling fatigue of a human operator, for example), the function can be an increasing (versus a decreasing) function.