The official language of Mexico is Spanish. English is usually spoken in the business world.
Have all printed material available in both English and Spanish. Business cards are essential and it would be an advantage to have the reverse printed in Spanish.
Most offices are open from 9:00am to 6:00pm but they can be open until 7:00pm from Monday to Friday. Most people leave for lunch around 2:00pm and take between 1 and 2 hours. Some offices have a longer lunch time and reopen from 6:00 to 9:00 pm.
More information can be found here.