When you arrive in Puerto Vallarta, you will be on Jalisco/Central Time. Once you head north, you will leave the state of Jalisco and cross into the state of Nayarit. While the time zone originally changed at the state line, a time zone change went into affect in 2010 within the Bahía de Banderas municipality, including the towns of Mezcales, Bucerias, Sayulita, San Pancho and Lo de Marcos. So once you pass Lo de Marcos (and head towards Los Ayala, Rincón de Guayabitos and La Peñita), be sure to turn your watches back one hour, as you will now be on Nayarit/Mountain Time.
Upon your return to the airport in Puerto Vallarta, remember that you will lose an hour as the time zone changes back to Central Time. Be sure to set your watches accordingly so you don’t miss your flight.