When flying from Palawan to Chiang Mai, the time of day you decide to fly out makes little to no difference towards the overall price you’ll pay on tickets.
Chiang Mai (CNX), located 3.1 km from the city center, is the airport you fly into when you book flights from Palawan to Chiang Mai.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Puerto Princesa Airport to Chiang Mai Airport flight would often be abbreviated as a PPS to CNX flight. El Nido Airport (ENI), Busuanga Airport (USU), San Vicente Airport (SWL) are other airports near this flight route and their unique identifiers/IATA codes.