Beaches and Cream is well themed and a difficult ADR to get. I too believe that an earlier buffet time might be too much food. But if this is where you want to go, adjust your dinner plans for a lighter meal.
On the other hand, if your real desire is Cape May for seafood buffet, as others have mentioned - why spend extra for dessert?
But if you must - Fountain inside Dolphin is about 1/2 mile stroll to other side of Boardwalk and might give enough time to walk-off a buffet dinner. While Fountain is not well themed, the ice cream may be a bit better. Fountain has option of table/counter service or take-a-way. Of course, there is ice cream along the Boardwalk too, albeit, without table service.