Bill is right. I say this as someone who has visited SWO 5+ times over the last 4 years and just finally visited Universal - both parks - just last month. Plan to spend time at Universal. You don't need to dedicate a day to SWO. Its a great park, I am a huge fan, but we always kind of run out of stuff to do there because while the B&Ms & Journey and Infinity Falls are great, that's really kind of it. If you want to hit coasters and don't care so much about animals, you can probably do SWO in like 2-3 hours if you get there at park opening.
Do yourself a favor and plan to spend more time at Universal, particularly IOA. It might be my favorite park ever, and I did not expect to have that opinion ahead of visiting in December, after years of just not really caring about Universal at all (no notable coasters that piqued my interest and whole lot of bitching from people about screen-based rides, etc). After spending one day 9am-7pm at both Uni parks, I only wish we had booked 2-3 days there. Seriously. While I'm kinda of ho-hum on the Studios park (I personally hated Rip Ride Rocket), Gringotts is amazing. So is Mummy but that's closed now. So if you want to ride Gringotts and try RRR for yourself then do the park hopper. But the real stars of the show are VelociCoaster and Hagrids. I was blown away by both. VelociCoaster is the greatest coaster on earth. Granted I'm a full blown Intamin fanboi and hadn't ridden any new ones in a few years so maybe it was just getting to ride those two back to back that made me blow my top, but I'm obsessed. And beyond that Universal -particularly IOA - is just awesome. Incredibly themed, clean, great ops, great staff, all the Potter rides are awesome (don't skip Forbidden Journey - amazing). We really loved everything about IOA. I cannot wait to go back and while we had an amazing trip all around (that also included SWO, Discovery Cove, Animal Kingdom and Funspot Orlando) my big regret was not booking 2+ days at Universal.
Did I mention VC is the best ever? Plan to spend as much time as you can there. And for the love of god don't skip Hagrids. I know some people will think I'm insane but its a top 10'er for me. I said what i said.