When I was stung in June, I immediately went to my Mexican neighbor. She squeezed lime juice over the sting, then placed the lime on the sting and wrapped it in place. She also fed me a clove of garlic and made me drink an "herbal" tea. I had no pain from the sting, just numbing. It took over 3 hours for me to get severe enough symptoms to seek medical assistance. I went to Melaque to the Centro de Salud and received an iv treatment.
Everything I read said symptoms should appear within an hour. Not sure if the neighbors treatment was the reason for the delay of sickness or not.