Enough background, now logistics, by mid-afternoon the zócalo bustles as contestants set up displays on tables in booths, end-to-end around three sides of the square. There is a viewing platform at the height of the tables about two meters distant. Booths are lit so viewing goes on between late afternoon and (you guessed it) fireworks. It’s hard to imagine anything happening without fireworks. Short of being there, you can view pictures here or at another website planeta which has loads of other information and pictures on Oaxaca.