Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Doha to Siargao Island as you normally would.
Doha Hamad Intl (DOH), located 8.8 km from the city centre, is the airport you fly out of when you book flights from Doha to Siargao Island.
This is defined as Doha Hamad Intl Airport (DOH) and Del Carmen Sayak Airport (IAO). Codes like Del Carmen Sayak Airport are often used to just call airports uniquely.