Pamela:
If you have a
park hopper option on your ticket, you can visit one park and then leave to eat lunch at a different one. But, since you asked, just because you can, might not be the best use of your day if that is all you plan to do at the second park, or especially if you plan to return to the first park.
The fastest time I've park-hopped was when I took the monorail from the Magic Kingdom to Epcot in about 30 minutes. But that is from the front of one park to the front of the other. To get to the restaurants, you'll need to add at least 15 to 20 minutes on that time estimate. If you're having to take a bus from one park to the other, say, Animal Kingdom to Magic Kingdom, the journey may take much longer. And keep in mind that you may have to wait on your transportation.
To make the most of your time, plan on staying to enjoy your second park after lunching there.
Wishing you a magical vacation!
Whitney