No, as I understand it, it's the entire state of Quintana Roo that now will follow "Tiempo del Sureste" under what is referred to under the law entitled "Ley de Sistema de Horario de los Estados Unidos Mexicanos" as passed 14 Dec 2014 in the legislative act known as "Ley de Husos Horarios en los Estados Unidos", and the Senate act of 2012.
They will follow DST as well. Pretty much what goes on on the U.S. East Coast will be concurrent throughout the state of Quintana Roo. "Tiempo del Sureste: UTC–5 (UTC–4 en verano)." as I think it ought to read.
Quintana Roo used this in the 1990s to justify their time zone with those of other Caribbean tourist destinations as well as certain cities in the USA (Miami and New York, among them).
Among other sources:
http://es.m.wikipedia.org/wiki/Husos...de_M%C3%A9xico
There has been opposition to this, but the strong support of state legislators and their supporters in the tourist corridor prevailed.