If you can attach a packaged workbook or sample data then you will get more precise answers for your problem.
Based on the above description I believe you have to use window_max. // Duration Calculated in hour
Sum(EventDuration)/Datediff('hour',Window_Max(MIN(Event Start Time)),Window_Max(MAX(Event End Time)))
//MAX(Event End Time)-MIN(Event Start Time) will not give you the total duration if you place the events in the rows, It will return the each individual event duration. So you have to use Window_Max function.
You're a genius.
Very many thanks
, Glad that solution has worked for you!