This is a very broad question but a good one. It all depends on the day you go and what you plan to do. If you go on a weekend, its probably not. But a less crowded day like a Tuesday or Wednesday maybe. If you want to do absolutely everything (shows, all animal exhibits, rides, character meet and greets and I assume sit down to eat once or twice) no one day is probably not enough. If your going for one reason say for example rides then yes one day is enough.
If you have not yet visited the park then you will want to plan for a 2 day experience. That way you will be able to relax and enjoy. If you attempt a one day blitz then that's what you will get... the since you had a great time but unable to fully remember all the fine details. Good luck
Yes, if you arrive early there. Plan the shows you want to see and check on the Sea World's webpage the times. I went in January, it was not full. I guess in July it's full.
Yes
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