I would think that you are going in the morning. This way is a little longer but with the mess on I-4 in the mornings, it will probably save you a lot of time.
Turn left leaving the Dolphin parking lot. At the set of lights (Buena Vista Drive), take a left. Follow that all the way down past Downtown Disney West Side, Pleasure Island and the Marketplace. You will take have to take a right onto Hotel Plaza Boulevard. Follow that to the end and take a left at the lights onto SR535 (Crossroads Shopping Center is directly in front of you at the lights). At the next set of lights (Palm Parkway), take a right. Follow that straight for about 3-4 miles. You'll come to a set of lights (Central Florida Parkway) where you'll take a right. Follow that straight about one half mile and the Sea World parking lot will be on your left. Total travel time should be about 15 minutes if you hit the lights right, 20-25 minutes if you don't.