We're doing the whale sharks this July, we did it in 2012. It's a long day, but worth it. You have to catch the 6:00 am ferry to Playa Del Carmen. Then an hour bus ride to Cancun. Then about 45 minutes to the whale sharks. Allow 3 hours to snorkel with the whale sharks. Then lunch at Isla Mujeres. Then an hour bus ride back to Playa Del Carmen. Then about an hour ferry ride. You get back to Cozumel about 6:30 pm. I said, it's along day but worth it!