When selecting multiple objects on screen, the designer can select a start time so that all objects appear at the same time. But if the multi selected objects have different start times, entering a common Finish time for all the selected objects is not allowed. It actually "adds" the time to the current time. If the designer wants the objects to leave the screen at the same time, every object has to be programmed with the same "Finish Time" individually. Many presentations bring objects on screen during narration at different times but need those same objects to leave the screen at the same time to make room for some other objects. Makes sense to allow the programmer to multi select and fill in a common Finish Time.
