I think the next approach will work:
Create data island with one field Intervals. Create chart with Intervals as dimension, and the next two expressions:
StartCount = COUNT(if(StartIntervalTime=Intervals, DataEventID))
EndCount = COUNT(if(EndIntervalTime=Intervals, DataEventID))
Warning: the performance maybe be poor with a large amount of data.
Hi Dan, In the above case you need to create common IntervelTime (In Link table if required) for both fields and use this new field as the Dimension. Similarly create the FLAG weather its start or end .