You can sample a little of everything in Yucatán [1] in five days, but you won’t be sorry to have a week or more. Budget at least two days for Mérida [2] itself, and at least another two to visit the ruins—one for the Puuc Route [3] and another to visit Chichén Itzá [4] and its surroundings.
If you love ruins, budget three or four days—that way you won’t feel rushed to get through them. Finally, leave a day for an outdoorsy trip, like visiting the flamingos in Celestún [5] or Río Lagartos [6], or swimming in cenotes.
Mérida is well known as one of Mexico’s hottest cities, with high humidity and average temperatures of 37°C (97°F) from April to July. The same months are blessed with almost daily rain showers, which provide cooling relief, and most travelers adapt quickly to the climate. However, families and older travelers should take special care.
Links:
[1] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan
[2] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan/merida
[3] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan/the-puuc-route
[4] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan/chichen-itza-and-piste/chichen-itza-archaeological-zone
[5] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan/celestun
[6] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan/rio-lagartos-and-san-felipe/rio-lagartos