Of course we don't know what gets edited out of these progs, but....
This task of catering for a large number of people who are on a tight timetable comes up every time! The contestants should be able to go with a few working ideas in their heads. Don't any of them have a work canteen? Could they ask the chefs there what recipes work for large numbers?
I know it's not as simple as taking a recipe for 4 and scaling it up, but they should have a few tricks up their sleeves e.g. some stewy type dish can be got ready a little bit early and won't spoil if it's cooked a bit longer, more liquid can be added if it's getting a bit dry. Nothing which needs last minute cooking. Those sorts of tricks.