Calculate duration for recurring event

Hi,

I've got a Calendar list where I need to show the duration for each entries. I've done this with other calendars already by creating calculated columns and using formula to calculate the time difference. However, the recurring event option was made hidden in those cases.

In this Calendar, I need to allow the recurring events. If the recurring option is used, the calculation shows the duration for the entire series instead of duration of each event. And I don't have the recurring event field available when creating the calculated field, so I can't make any exception either.

Is there any way to calculate the duration for each recurring events.

Thanks,