If you have to be at the airport around 9am, I assume your flight departs around noon.
Therefore, if staying your last night on the cayes, I'd suggest a morning flight from the caye to the International airport -- easy. Next best would be a water taxi to BC. Early morning boats to BC give you enough time to get to the airport by 9am. For me, either option would be better than a night in Belize City.
If your final night is on the mainland, an early morning departure from San Ignacio (or anywhere nearby) will get you to the airport by 9am. You'll have to arrange transportation with a transfer service. I wouldn't want to be travelling by road from anywhere farther south. If coming from Placencia, check Tropic Air for flights to BZE.
Edited: 2 years ago