Krabi Airport is not on or near the water. For example it is between 45 minutes and one hour from the Sheraton Krabi Beach. Krabi town is closer, but still a fair distance from the airport. As suggested previously, stay overnight and continue in the morning if the time from arrival to boat is constrained.

Also as suggested, buy the Express Boarding option on AirAsia. Especially good for those of us who are queue and middle-seat adverse. Sitting at the front of the plane gets you to immigration first if you move along. Otherwise you will be overtaken by the hordes, so move briskly along.

Baggage handling is fairly prompt as they are trying to turn the aircraft quickly so there should not be a long wait for luggage.

Also do not expect on-time performance especially later in the day.