The scheduled departure times are determined by Sea Coach/Sea Bird and the Airline personnel. It is timed to allow the passenger arrive at the airport with enough time to complete all necessary travel procedures at the airport without getting there too early. Both companies set their ticket prices at 40$ and the trip will last around 30 minutes. The difference will be their departure/arrival in Freetown. Sea Coach arriving at Aberdeen (70 Sir Samuel Lewis Road) and Sea Bird arriving in Murray Town (36 High Broad Street).
More information on:
https://www.seacoachexpress.com/ticket-siera-leone/
http://www.seabirdsl.com/
Ferry
The ferry is also an option in order to get from the airport to Freetown. This will be the cheapest option (prices around Le 5,000 excluding vehicle costs) but will certainly not the quickest option neither the most convenient. Currently there is only one operational ferry so timings might vary.