Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Pullman to Manila as you normally would.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Pullman Moscow Regional Airport to Manila Ninoy Aquino Intl Airport flight would often be abbreviated as a PUW to MNL flight.