Time: Calculate Duration, Start and Finish Time . Duration is the difference between the start and finish times for an event. Duration calculations have a triadic relationship as there are three parts to each problem – a start time, a finish time and the duration. . These three components of a duration problem can be thought of as a part-part-total relationship where the start time is a part, the duration is a part and the finish time is the total. Any of these 3 components of the problem (start