What grit sandpaper scratch was being corrected and how many square inches of paint were each of the panels?
I think a good protocol would be to start at the same time. When one person gets to a finish they think is acceptable they stop. Everyone else stops and at that point everyone decides if they want to be judged right then or work some more. If people want to continue, they can, but if when they quit if the finish they've got beats the one who finished first, that person can continue, till they have taken the same amount of time as the person who took longer.
For me, it is about time and quality. There has to be a way to account for both.
Thanks,
Robert