The following graphic shows the time spent in actual competition (racing/rallying) by class and class grouping:

The original document is a spreadsheet where I can change values in the two coloured columns. The first table is sorted by total race time (lowest to highest), the second to match our current class groupings. In this graphic I've set the number of laps to give a total competition time of 41-51 minutes for each class grouping. Of course we can adjust these as needed to produce different results by simply changing the number of laps and races.
Let me know your thoughts...
Gordon