The last time we went to Roatan (Reef House), we arrived about 6 PM after travelling all day, had diner and then went on a night dive on their house wall... Awesome way start the vacation.
As others have said, it's possible that they are allowing for missing baggage, or allowing administrative time etc. However, I think Bert has nailed it up above. They want to see you in shallow water first. Perhaps you can convince them of your abilities by showing them a log book with a few gazillion relevant dives in it.