Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Surabaya to Palau as you normally would.
Surabaya Juanda (SUB) is the airport you will fly out of if you book a flight from Surabaya to Palau. It is only a 15.0 km journey to Juanda (SUB) from Surabaya’s city centre.
This is defined as Surabaya Juanda Airport (SUB) and Koror Airai Airport (ROR). Codes like Koror Airai Airport are often used to just call airports uniquely.