Hi Setzer & welcome to SB. Your profile says Not Certified, right? So you are looking for a Discover dive...?
Costa Maya is more of a marketing term, I think. Do you know which port you will actually visit, the hours in port - and what time zone? Ships stay on the time zones of their boarding ports, i.e. Galvestion, Miami, etc.
There is a Costa May port by name, altho the term is more general. That port has an artificial village build to amuse boat people and get as much money as possible for the cruise line rather than the locals. It's about 100 miles south of Playa del Carmen near
Mahahual and
Xcalak not far from the Belize border. There is some diving done there, but not a lot, and not beginner diving I don't think. Long story...
I'd never been that far south inside Mexico. It'd probably be a neat area to explore if one had several days. For a cruise stop, who knows...?