Actually I was just at Seaworld from WHR last month. It took us about 15 minutes to get there from WHR, not counting the long lines to get into the parking lot at Seaworld. To get onto I-4 is all of 2-3 minutes, even at a peak time it wouldn't take you any longer than that, very easy, there's 2 traffic lights on the way, the first of which is a right hand turn anyhow.
Late that afternoon (this was on a Saturday) we had to go back to WHR to take our stroller back before heading to the airport, again, it was 15 minutes. (We had already checked out of our home).
SeaWorld was pretty fun and entertaining by the way, and you can buy a ticket now that's good for admission for the rest of the year for the same price as a 1 day ticket, we did, so plan on going back this fall some time.
We saw Shamu, and Clyde and Seymour was a great show too! Our DS was not tall enough for the Kraken roller coaster though much to his disappointment (54"). They also have a good play area for littler kids we spent some time in and they enjoyed.