A few pointers, if your plane arrives in Cancun after 11 pm the bus station at he airport will be closed. You will have to take a taxi to the bus station in Cancun. The buses from Cancun or Playa leave about every 90 minutes starting at around 4;30 am. very nice buses, movies etc.Their are some nice reasonable Hotels in Old Cancun near bus station $20 to $25 a nite. Its about 5 to 5 1/2 hours to Chetumal. There is really no need to pay for any service to meet you at the boarder. The buses from Chetumal to Belize leave about every hour, they stop for you to go through customs and will wait on the other side, if you get delayed another bus will be by soon. These buses are not as nice, but OK. You can then make the choice to get off at the Corozal Airport, or town to take the water taxi, be aware it only runs once a day and may not run everyday. Or you can go all the way to Belize City, this takes between 3 and 5 hours depending on all sorts of things.The last water taxi leaves the city at 4;30, 5;30 to Caye Caulker only. We have done this many times, its simple. I have never heard of anyone using a transfer service, sounds like a rip off to me, but I may be wrong, I just cant see what they would provide except taking your money. It is going to be very close if you leave Playa at 8am to catch the 3pm water taxi from Corozal, Its more like 6 hour if you have to go to Airport in Chetumal, that makes it 2 oclock already, big risk to get through customs and to your destination in less than an hour, always give yourself time for the unexpected.