Becky, if you aren't in a big rush to get to AC, perhaps a night spent on your first day. Get a taxi from the airport, grab a nice room in a good part of the city, like the Colton House ( recommended ) and it's right in the heart of all of the interesting parts of Belize City.
Look at the map that's offered on the Colton House web site and see how close everything actually is, we walked to our room ( Colton House ) in about 5 minutes from the water taxi and the Raddison Fort George is across the street from the Colton House, and just a couple doors away from the Great House. LOVELY area.
Of course, this is taking one night away from AC, but it was certainly worth our stay for our last night in Belize. We only wished we had the time, that night, to go to some of the interesting places nearby. Next time !
Think it over.
It's easier to do when you don't have to spend part of the day on the water and then, yet, have to return to the island.
Just a thought.