How long before a fight should a boxer break camp and go to the city where the fight is taking place? Dose it make a difference how far he must travel? How long dose it take to get used to time zone changes? What about a different climate and foods than he is used to?
Ali and Foreman spent months training in Zaire for their showdown... And then there are idiots like Froch who fly in the day before.
Really it comes down to a lot of factors specifically climate, time zone, and altitude. Train in California and fighting in Vegas no big deal come the day before or something. Train in Minnesota and fighting in Mexico City you probably want to give yourself a few weeks or months to get prepared. Ultimately I don't think food would matter that much since for most places it wouldn't be too difficult to get food that you are more accustomed to.