For the most part and to my knowledge, I know a lot of competitions have time blocks for groups so prep/single gender choirs are first to go and then 1A, 2A, 3A, 4A, 5A are to follow. Some competitions base it off of registration and how far in advance they registered. So if a 3A choir registers really early and the time block for that category is 2:30-5:00 then they get to pick a time from that block, does that make sense? And yes, sometimes they are randomly picked but I don’t know how common that is. I’m not saying this competition based it off registration but it does appear that they have single gender choirs going first and the bigger groups to follow with some mixed in.
Sorry, I should have been more specific. For the earliest time block - single gender, I was curious about that. I ask because some schools are traveling farther than others.