Yes, you have time to see plenty of Coral World, have a great snorkeling and playing time on Coki beach, and then some!
It was the best day! We took a taxi from the dock, the driver gave us discount coupons which ended up saving us as much as his fare! We got a locker in Coral world for our snorkel gear and picnic lunch (compliments of room service the night before) and came and went as we pleased. Coral world had a nice web site to check out ahead of time.
http://www.coralworldvi.com/ There's so much to do there! We went parasailing from the dock just on the other side of Coral World from Coki. We used Caribbean Watersports (I think it was called, there was a link from the Coral World site). They'll e-mail you the brochure, very nice staff. Their weight requirements worked better for us than
Castaway Cay's so my youngest was able to tandem with me. We had a boat just to our own family and the kids got to drive it back. PM me for more details if interested.
Oh, a favorite souvenir was from the little shopping 'huts' a little ways up Coki beach. Between the dive shop souvenir huts, is a cool 'rasta' guy, who will take a digital picture of you, (we even got his helper to hike back to "our" spot to take our family picture), then he puts whatever caption, date, cropping, adjustments, etc., on it that you want before printing it on transfer paper. (He really knew his way around that computer) He then presses it with one of those major industrial presses onto a T-shirt or canvas bag. We picked the canvas bag with our picture on one side, and a cool 'crackle/textured' style image of the Disney Magic on the other.
That was our favorite day and I'd do it all again without changing a thing. Have fun!