14 days admission to both SeaWorld and Aquatica (SeaWorld's waterpark) is included with regular admission to Discovery Cove. Generally, the only time SW and AQ are not included with your DC day is if you book as a passmember (which gives you a significantly discounted price). You have to have an annual pass to Seaworld, Aquatica or Busch Gardens in order to quality for the passmember pricing, though, so I'm guessing that doesn't apply to your situation.
Your SW and AQ admission can be used either before or after your DC day, or a combination of both. A 14 day parking pass for both parks can be added to your DC reservation for an additional $30 with the 30 days prior to your visit. You can't do this online, you have to call DC and ask for it.
If you visit DC first, you use your DC ID badge for your entry into both SW and AQ. If you choose to visit one of the other parks first, then you use the voucher you are emailed by SeaWorld Parks & Recreation for your entry.
There is more than enough to keep you busy at DC from open to close. In fact, if you are like most people, you will find the day flies by and you wish you had MORE time. There's snorkelling in the Grand Reef, visiting the birds in the free flying aviary, watching the marmosets and the otters in the Freshwater Oasis, and the Wind Away River takes about 20 minutes just to do one full rotation. There's hammocks to relax in, unlimited breakfast, lunch, snacks, and beverages (including alcohol), and often even a random animal encounter or two (we have 'met' both a sloth and an armadillo). And of course....there's your dolphin interaction.
SeaWorld and Discovery Cove are very close together. There's a shuttle that runs between the two parks, if I remember correctly. Parking is free at Discovery Cove, but a charge at both SW & AQ (which is why I mentioned the parking pass add-on....well worth it if you plan to visit each park more than once).
There are some great threads which are very helpful over on the SeaWorld & Discovery Cove forum here on the boards. You can get there by clicking here:
http://www.disboards.com/forums/sea-world-discovery-cove.32/
