Mum's ODE is pretty much the same. She splits the classes so each arena has the same number of people through it (means some classes are split in an apparently odd way, but it's so each judge does the same mount of work!). Does the tests for each arena at 6 minute intervals with a 20 minute break every 2 hours.
Then she starts with the smallest class, and then for the last competitor their SJ is 35 minutes after their dressage, and their XC is 35 minutes after that and then work backwards. Then repeat ad nauseum for each class.
The put in 'priority' riders (multiples/ mum and daughter/ with someone so close times/ late/ early) so they're sorted, an then slot the rest in.
Takes mum about 6/ 8 hours in total of jiffling around so we start and finish in the light!