Setting the duration of the external event when it is dragged to calendar

Many times (most, I believe) when we use the option to drag external events to the calendar, we want different events have different durations. 

Currently we can not individually set the duration of the event dragged while it still is not dropped, which causes a problem, showing the helper with different duration of the event. 

I propose that a setting be added so we can set the duration of the event according to the element that is being dragged.