You should be able to hop a bus from the Animal Kingdom to the Grand Floridian. You should allow about 20 minutes possible wait time for the bus, and then a 20 minute or so trip to the hotel, possibly stopping at the Contemporary and the Polynesian resorts on the way. I would allow at least 45 minutes from the time you get to the bus stop to the time you're walking into the hotel to be safe, maybe even an hour if you want to be early.