Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Palawan to Siem Reap as you normally would.
If you book a flight to Siem Reap from Palawan, you will be flying to Siem Reap, which is the city’s only airport. Siem Reap (REP) is located 7.4 km from the center of Siem Reap.
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 Siem Reap Airport flight would often be abbreviated as a PPS to REP flight. El Nido Airport (ENI), Busuanga Airport (USU), San Vicente Airport (SWL) are some additional IATA codes for airports related to your trip.