The simplest way to handle this, is to not have your staff go off schedule at the end of the day but simply let them work until they run out of patients for the day as defined by your arrival schedule. Close examination of your hourly utilization plots will tell you how long staff needed to work. There are more formal ways to capture the overtime hours worked if you're willing to put in the extra modeling effort. The solution depends on how your arrivals are being modeled, whether you need to run consecutive days, and who goes home when.
