You've got a lot of options for operators that do day long snorkel trips with a beach BBQ. Your resort can schedule for you and make recommendations. We went with Seaduced because we like the company - Elito is the owner and he's good people. Their trip is more expensive than some of the others - we were in vacation mode when we booked and I'm frankly not sure if the cost was $80 or $90 per person.
Seaduced's trip is on a good sized catamaran, however there were only about 12 passengers. Due to the size of the boat and the time that would be required, Seaduced doesn't pick up passengers at docks - the trip leaves from Ramon's pier.
The trip left about 9:30. Our group voted to make the trip to Basil Jones faster by going outside the reef. That made the journey a bit rougher, but a lot of fun. Four of us got out on the trampoline net at the front of the boat to enjoy the sun and breeze. We likewise got thoroughly soaked from splashing waves. I'm sure we had more fun than the folks that sat farther back....
The trip north to the former Basil Jones timeshare resort took about an hour, (it's about 22 miles north of San Pedro). Elito's brother recently purchased the failed resort and is in the process of finishing it. We ate lunch in the building that will be the resort's bar and restaurant.
We had a lot of time before and after lunch to snorkel out to the reef (very close to shore that far north). About 3:00 PM we left for San Pedro - most of the way under sail power - arriving about 5:30.
We've done other snorkel / beach BBQs on smaller faster boats. On those trips we got more snorkel stops and the trip up and back was faster. On the other hand, even when Elito needed to use the diesel power, the catamaran was very peaceful and relaxing. The boat has a nice galley and men / women's heads. So, although slower, it was totally enjoyable. Other beach BBQs we've had have been cooked over a coconut husk fire, right on the beach. With Seaduced, our lunch was excellent, but much of the food was pre-prepared. (Elito's wife, Rebecca, makes way killer brownie cupcakes - they're almost debilitating....)
So, there's my two-bits - decide what type of trip you want and go for it - you're going to have a great time.