We just did what I consider a "quick trip" through SeaWorld. I thought we'd have 6-7 hours... but really had from 11am-7pm... and that was nice!
But if you fly in... will your flight arrive on time? will you have to wait on luggage? how long will it take to get your rental car? All unknown until you arrive. I think it would stress me... cause I would feel the clock ticking!
Additionally, who knows about traffic and driving times based on what day you'll arrive... someone else might give you a good reference on it.
Travel days can be very tiring anyway. Even the hotel check in can be frustrating.
For us, on that day, I think we would enjoy some entertainment not tied to a DAY ticket! Like if the resort where you are staying has a cool pool, enjoy it! Or make a reservation at a FUN restaurant like Whispering Canyon or if you have kids that love the characters... one of those type meals. Then, go somewhere to watch the fireworks from outside the parks... Contemporary, Polynesian, Boardwalk.
I guess if you felt it was the ONLY way you ever were going to get to SeaWorld... I'd do it. But I would play it by ear... be flexible... and know that if travel doesn't go smoothly... you could change your plans. It's a good excuse for another trip!
Good luck... and let us know what decide!