Timing
You should plan to spend at least five days in the Yucatán. It's best to start your trip with a few days in Mérida. (Weekends, when some streets are closed to traffic and there are lots of free outdoor performances, are a great time to visit.) You should also budget enough time to day-trip to the sites of Chichén Itzá and Uxmal; visiting Mérida without traveling to at least one of these sites is like driving to the beach and not getting out of the car.