Chiapas [1] is a big beautiful state, with a wide array of archaeological, colonial, cultural, and natural attractions; to see and do it all would take months, or more. That said, for most travelers seven days is enough to get a quick taste, while two to three weeks let you truly savor what the state has to offer.
Budget two to four days for Palenque [2] and the Río Usumacinta Valley [3]—one day for Palenque ruins, and another one to three days for outlying waterfalls and archaeological sites.
San Cristóbal [4] and the Lakes Region [5] can easily occupy another three to six days—between San Cristóbal itself, the nearby indigenous villages [6], and outings to Comitán [7], Lagunas de Montebello [8], and beyond.
Tuxtla Gutiérrez [9] and the Pacific coast include a handful of must-see sights—especially Cañón del Sumidero [10], near the town of Chiapa de Corzo [11]—but otherwise are visited only by travelers with plenty of time or specific interests.
Links:
[1] http://www.moon.com/destinations/chiapas
[2] http://www.moon.com/destinations/chiapas/palenque/palenque-town/palenque-archaeological-zone
[3] http://www.moon.com/destinations/chiapas/the-rio-usumacinta-valley
[4] http://www.moon.com/destinations/chiapas/san-cristobal-de-las-casas
[5] http://www.moon.com/destinations/chiapas/the-lakes-region
[6] http://www.moon.com/destinations/chiapas/san-cristobal-de-las-casas/villages-around-san-cristobal
[7] http://www.moon.com/destinations/chiapas/the-lakes-region/comitan
[8] http://www.moon.com/destinations/chiapas/the-lakes-region/eastern-chiapas/parque-nacional-lagunas-de-montebello
[9] http://www.moon.com/destinations/chiapas/tuxtla-gutierrez
[10] http://www.moon.com/destinations/chiapas/tuxtla-gutierrez/around-tuxtla-gutierrez/parque-nacional-canon-del-sumidero/canon-del-sumidero
[11] http://www.moon.com/destinations/chiapas/tuxtla-gutierrez/chiapa-de-corzo