Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Manila to Decatur, Illinois as you normally would.
Related info for your journey
Useful info, stats and facts about Manila to Decatur flights.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Manila Ninoy Aquino Intl Airport to Decatur Arpt Airport flight would often be abbreviated as a MNL to DEC flight.