Dear All,
I have an upcoming conference in Cancun at the end of September, and I'll be going there with my entire family (wife and two adult kids, ages 18,22).
After the conference ends we have 4 days until our flight home, which is on 11pm on the fourth day, and so after a few days of resting in Cancun (and probably doing one or two day trips from there as well), we would like to visit some other parts of Mexico, and we are currently considering doing the following:

Day 1 - flying from CUN to Tuxtala Gutierrez
Day 3 - AT the end of day (7pm), flying from Palenque to Mexico City
Day 4 - day trip of Mexico city, flying home at 11pm

How does it look to you? In Chiapas we would like to see mostly Palenque, Agua Azul, etc. The reason I'm looking to do the flight on day 3 from Palenque to MEX (instead of from Tuxtala Gutierrez) is simply to save time travelling, and it so happens that there is a direct flight that day.
Are these good dates for visiting these places? If not, any other recommended places to visit?
Also, any recommendations for good travel agencies to help us set the trip in Chiapas (with guide, transfers, activities, etc.)

Thanks!